Initialize structured logging library

[henrylee97]

Summary

• Initialize scribe as a value-based structured logging library for OCaml.
• Add the core Scribe API with levels, structured fields, events, logger values, and abstract sinks.
• Add scribe.sinks with concrete sink modules for JSON lines and noop sinks.
• Add Alcotest-based tests and README usage examples.
• Add ocamlformat configuration, GitHub Actions CI, Dependabot, and repository convention docs.

Details

• Core library:

  • Scribe.Level
  • Scribe.Field
  • Scribe.Event
  • Scribe.Sink
  • logger helpers such as create, noop, with_field, warn, info, and debug

• Sinks:

  • Scribe_sinks.Json.channel
  • Scribe_sinks.Json.stderr
  • Scribe_sinks.Noop.create

• Tooling:

  • profile = janestreet via .ocamlformat
  • CI runs build, tests, and formatting checks on main and PRs targeting main
  • Dependabot tracks GitHub Actions updates

Verification

• dune build @fmt
• dune build
• dune runtest
• dune build @install