Add CodSpeed continuous performance benchmarks

[codspeed-hq]

Summary

This PR integrates CodSpeed for continuous performance monitoring of ext-php-rs core operations.

What's included

• Criterion benchmarks using the CodSpeed compatibility layer (codspeed-criterion-compat), added as a new [[bench]] target in the main crate with the embed feature.
• CodSpeed GitHub Actions workflow (.github/workflows/codspeed.yml) that runs on pushes to master, pull requests, and manual dispatch. It uses OIDC authentication and simulation mode for reproducible measurements.
• CodSpeed badge added to the README.

Benchmark coverage

The benchmarks test performance-sensitive paths across the FFI boundary:

• PHP eval: simple expressions, string concatenation, array creation
• ZendHashTable: sequential push, string-key insertion, lookup by key/index, iteration over 100 entries
• ZendStr: short and long string creation
• Zval: integer set/read, string round-trip

All benchmarks use Embed::run() to start an embedded PHP SAPI, testing the actual runtime behavior of the library rather than synthetic stubs.

CI workflow details

The workflow mirrors the existing benchmark CI setup for PHP and LLVM/Clang dependencies:

• PHP 8.4 with libphp-embed for the embed feature
• LLVM/Clang 17 for bindgen
• cargo-codspeed for building and running benchmarks in simulation mode

Next steps

• Once merged and the first run completes on master, CodSpeed will start reporting performance diffs on subsequent pull requests.
• The benchmark suite can be extended over time to cover additional operations (e.g., closures, object property access, class instantiation).

[coveralls]

Coverage Report for CI Build 24471981668

Coverage decreased (-0.02%) to 65.871%

Details

• Coverage decreased (-0.02%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 3 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

3 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
src/internal/mod.rs	3	0.0%

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Coverage Stats

Relevant Lines:	12995
Covered Lines:	8560
Line Coverage:	65.87%
Coverage Strength:	32.96 hits per line

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💛 - Coveralls

[codspeed-hq]

CodSpeed setup failed

The CodSpeed benchmark setup for ext-php-rs exhausted all 3 retry attempts due to Rust compilation errors in the benchmark file. The benchmarks use Embed::run() which requires FnOnce() -> R + UnwindSafe, but capturing &mut Criterion in the closure violates this bound. The correct fix (wrapping the entire closure with AssertUnwindSafe instead of just the reference) was implemented locally but could not be pushed because the retry limit was reached. The fix commit (04d289a82) changes Embed::run(|| { c.bench_function(...) }) to Embed::run(AssertUnwindSafe(|| { c.bench_function(...) })) for all 12 benchmark functions. This is a straightforward code fix that would resolve the build on the next attempt.

[github-actions]

Bencher Report

Branch	codspeed-wizard-1776277848593
Testbed	PHP 8.4.20 (cli) (built: Apr 11 2026 00:52:25) (NTS)

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