feat(fetch_azure): adapt fetch HttpClient to Azure's HttpClient

[martintmk]

Summary

Adds two crates that adapt Oxidizer building blocks to the Azure SDK abstractions, built directly on typespec_client_core 1.0.0 (the crate that defines the HttpClient and AsyncRuntime traits that azure_core re-exports):

• fetch_azure — AzureHttpClient implements typespec_client_core::http::HttpClient on top of a fetch::HttpClient transport.
• anyspawn_azure — Runtime implements typespec_client_core::async_runtime::AsyncRuntime on top of an anyspawn::Spawner (spawning) and a tick::Clock (sleeping). With the optional azure-identity feature it also implements azure_identity::Executor, running developer-credential commands on the spawner.

fetch is depended on without enabling any of its features.

Details

• AzureHttpClient converts a typespec Request (method, URI, headers, and bytes or seekable-stream body) into a fetch request, executes it, and maps the fetch response back into an AsyncRawResponse with a streamed body. Empty bodies and byte bodies avoid copies; non-UTF-8 response headers are skipped (matching the built-in reqwest transport). Build errors map to DataConversion; transport errors to Io.
• Conversions: From<fetch::HttpClient> and From<AzureHttpClient> into Arc<dyn HttpClient>; From<Runtime> into Arc<dyn AsyncRuntime>.
• Runtime spawns tasks wrapped in futures::future::Abortable so cancellation wakes pending waiters; sleep uses tick::Clock::delay.
• Examples: azure_transport (transport round-trip) and blob_list (transport + anyspawn_azure executor + DeveloperToolsCredential, listing blobs on tokio).
• Integration tests + doctests; client.rs and runtime.rs are each at 100% line/region coverage.

This mirrors the in-tree reqwest adapter shipped by typespec_client_core.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (963e015) to head (3438550).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #494    +/-   ##
=======================================
  Coverage   99.9%   100.0%            
=======================================
  Files        336      338     +2     
  Lines      24829    24932   +103     
=======================================
+ Hits       24818    24932   +114     
+ Misses        11        0    -11     

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[github-actions]

⚠️ Breaking Changes Detected

error: failed to retrieve local crate data from git revision

Caused by:
    0: failed to retrieve manifest file from git revision source
    1: possibly due to errors: [
         failed to parse /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/1f0b5970b95b02ee08d19ac3d38733fabb2e06f6/Cargo.toml: no `package` table,
         failed when reading /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/1f0b5970b95b02ee08d19ac3d38733fabb2e06f6/scripts/crate-template/Cargo.toml: TOML parse error at line 9, column 26
         |
       9 | keywords = ["oxidizer", {{CRATE_KEYWORDS}}]
         |                          ^
       missing key for inline table element, expected key
       : TOML parse error at line 9, column 26
         |
       9 | keywords = ["oxidizer", {{CRATE_KEYWORDS}}]
         |                          ^
       missing key for inline table element, expected key
       ,
       ]
    2: package `anyspawn_azure` not found in /home/runner/work/oxidizer/oxidizer/target/semver-checks/git-origin_main/1f0b5970b95b02ee08d19ac3d38733fabb2e06f6

Stack backtrace:
   0: anyhow::error::<impl anyhow::Error>::msg
   1: cargo_semver_checks::rustdoc_gen::RustdocFromProjectRoot::get_crate_source
   2: cargo_semver_checks::rustdoc_gen::StatefulRustdocGenerator<cargo_semver_checks::rustdoc_gen::CoupledState>::prepare_generator
   3: cargo_semver_checks::Check::check_release::{{closure}}
   4: cargo_semver_checks::Check::check_release
   5: cargo_semver_checks::exit_on_error
   6: cargo_semver_checks::main
   7: std::sys::backtrace::__rust_begin_short_backtrace
   8: main

If the breaking changes are intentional then everything is fine - this message is merely informative.

Remember to apply a version number bump with the correct severity when publishing a version with breaking changes (1.x.x -> 2.x.x or 0.1.x -> 0.2.x).

[heaths]

The only place I should see "typespec*" is in Cargo.lock.

[heaths]

Use azure_core. Forget typespec_client_core and below exist. Everything is re-exported from azure_core. It's an initiative we had to support but likely won't happen.

[heaths]

azure_core. We don't talk about typespec* crates.

[heaths]

I know we devs are bad at naming variables, but is __linkN really the best convention? Why not something more descriptive that is easier to associate should you need to fix something. And if you only refer to them once, why even have links. In fact, __link0 an __link3 are dups.

[heaths]

Last time I'll mention it, but azure_core. That depends on - and re-exports all of - typespec_client_core and typespec so maybe they are still needed here as transitive dependencies, but typespec* should not appear in any docs or Cargo.toml files.

[heaths]

You put your .ico in LFS but not you .png?

[heaths]

Probably should do something with it. This sample isn't inherently useful.

[heaths]

Why does your elided sample func return an Arc? Seems unnecessary.

That said, elsewhere, you should state the reason the Azure SDK wants an Arc is to promote sharing. Same is true of HttpClient, Policy, and TokenCredential traits. Our pattern of having their concrete implementation constructors return an Arc isn't bad Rust code. It's intentional to promote sharing. Most TokenCredentials, for example, share an endpoint/token cache and reduce network calls. Same is true across all the Azure SDK languages - but all of them (besides C++) are ref-counted so get it for free.