#33: embed Rust atoms into objects

[RAprogramm]

Closes #33

What this adds

Rust atoms that can be embedded into objects: a source string is compiled into a
shared library at run time, loaded, and called during dataization.

Module	Responsibility
src/rust_atom.rs with compilation and execution	writes a throwaway Cargo project for the atom, builds it as a cdylib, loads the symbol and calls it
src/universe.rs with operations and cache	the bridge an atom gets to the object graph, backed by SODG — vertices, data, labelled edges
src/rust_engine.rs	ties the two together: compile, keep, execute by name
build.rs	builds the fixture libraries the tests load, including a deliberately mis-named symbol for the failure path

Each generated atom crate is its own Cargo project on edition 2024 with
crate-type = ["cdylib"], which is independent of the edition phie itself
uses. Two dependencies are added: sodg for the graph and libloading for
dynamic loading.

Scope

This branch deliberately touches nothing outside the feature. .github/ and
.gitignore are byte-identical to master, and Cargo.toml gains only the two
dependencies. The coverage migration that used to travel with this branch now
lives on its own in #136, so the two pull requests cannot conflict, in either
merge order.

phie also stays on edition 2021 here. An earlier revision of this branch moved
it to 2024, which was neither necessary for the feature nor free: the pinned
cargo-tarpaulin 0.22.0 in CI cannot parse that edition, so the branch would
have depended on #136 landing first. The four let-chains that needed 2024 are
rewritten as nested conditions, and the edition bump can be its own issue later.

Verification

Run locally on this branch, after merging current master into it:

Check	Result
cargo test	393 tests pass
cargo fmt --check	clean
cargo clippy	clean, and also clean with --all-targets, which covers the test code
target/debug/fibonacci 7 10	prints 21 and 210
reuse lint	50 of 50 files carry copyright and licence
copyright notice in every new file	present, matching LICENSE.txt
actionlint, yamllint --strict, typos	clean

libloading is upgraded from 0.8 to 0.9, the current release, with the suite
still green.

[hanMaster]

@RAprogramm tarpaulin error: unknown variant '2024', expected one of '2015', '2018', '2021'.
Looks like right now the only way to fix failed check is to move to version 2021 since there are now new version of tarpaulin

[RAprogramm]

@RAprogramm tarpaulin error: unknown variant '2024', expected one of '2015', '2018', '2021'. Looks like right now the only way to fix failed check is to move to version 2021 since there are now new version of tarpaulin

@hanMaster Thanks for catching this! You're right about the edition 2024 issue.

I recommend switching to cargo-llvm-cov instead of tarpaulin. It's the officially recommended tool for Rust code coverage and fully supports edition 2024.

Why cargo-llvm-cov:

• Full edition 2024 support
• Uses LLVM's source-based coverage (more accurate)
• Actively maintained
• Official Rust tooling recommendation

Alternative: Update tarpaulin from 0.22.0 to latest stable 0.34.1 (released Oct 2025), but edition 2024 support is not confirmed.

I can implement cargo-llvm-cov if you approve this approach. What do you think?

[hanMaster]

@RAprogramm I think cargo-llvm-cov is most suitable now for test coverage.
@yegor256 what do you think?

[hanMaster]

@yegor256 ?

[yegor256]

@hanMaster unfortunately, I'm not an expert :( What's your opinion?

[codecov]

Codecov Report

❌ Patch coverage is 97.07602% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.06%. Comparing base (6025413) to head (2d1b427).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/rust_atom/compilation.rs	94.59%	2 Missing ⚠️
src/rust_atom.rs	90.00%	1 Missing ⚠️
src/rust_engine.rs	96.15%	1 Missing ⚠️
src/universe/operations.rs	97.56%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
+ Coverage   94.09%   95.06%   +0.97%     
==========================================
  Files          14       21       +7     
  Lines         711      872     +161     
==========================================
+ Hits          669      829     +160     
- Misses         42       43       +1     

☔ View full report in Codecov by Harness.
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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[hanMaster]

@yegor256 as I said before, I think cargo-llvm-cov is most suitable now for test coverage.

[RAprogramm]

@yegor256, please, check this out

[RAprogramm]

Refreshed this branch so that it no longer collides with anything.

• Merged current master in, so the branch is up to date.
• Moved the coverage migration out into #108: migrate coverage from tarpaulin to cargo-llvm-cov #136. This branch now leaves .github/ and .gitignore byte-identical to master, so the two pull requests cannot conflict in either merge order.
• Reverted the edition bump to 2024 and rewrote the four let-chains as nested conditions. That bump was not needed for the feature, and it made the branch depend on #108: migrate coverage from tarpaulin to cargo-llvm-cov #136, because the pinned cargo-tarpaulin 0.22.0 cannot parse edition 2024.
• Made cargo clippy --all-targets clean, which the previous revision was not, and upgraded libloading to 0.9.

393 tests pass, and fmt, clippy, reuse, actionlint, yamllint and typos are all clean locally. @yegor256 @hanMaster, this one is ready for review on its own now.