Add CodSpeed performance benchmarks

[codspeed-hq]

Summary

This PR sets up continuous performance testing with CodSpeed for the uutils/grep project, providing automated detection of performance regressions on every pull request.

Changes

Benchmark suite (benches/grep_bench.rs)

15 benchmarks covering the core performance-critical paths:

Pattern compilation (5 benchmarks) -- measures regex compilation cost across all supported modes:

• Fixed string, basic regex, extended regex, Perl regex, and multi-pattern compilation

Line matching (8 benchmarks) -- exercises the main matching hot path with different configurations:

• Fixed string match (hit and miss), extended regex match, case-insensitive match, inverted match, word boundary match, multi-pattern match, and long line matching

Throughput scanning (2 benchmarks) -- simulates realistic log file searching over 1000 lines:

• Fixed string scanning and regex scanning

CI workflow (.github/workflows/codspeed.yml)

A GitHub Actions workflow that runs benchmarks on every push to main and on pull requests, using CodSpeed's CPU simulation instrument for deterministic, low-variance measurements.

Visibility changes (src/lib.rs)

Internal types (Config, Matcher, RegexMode, etc.) are marked pub with #[doc(hidden)] so they can be accessed from the benchmark harness without polluting the public API documentation. A GlobSet::new() constructor was added for the same purpose.

README badge

Added a CodSpeed performance badge alongside the existing badges.

Next steps

• After merging, CodSpeed will automatically start tracking performance on subsequent PRs and pushes to main.
• Performance results and flamegraphs will be available in the CodSpeed dashboard.
• Additional benchmarks can be added to benches/grep_bench.rs as needed (e.g., file I/O throughput, recursive directory scanning).

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 15 new benchmarks were detected.

You will start to see performance impacts in the reports once the benchmarks are run from your default branch.

Detected benchmarks

• fixed_string: 19.5 µs
• long_line_hit: 27.9 µs
• fixed_string_miss: 5.2 µs
• inverted_match: 5.3 µs
• multiple_patterns: 39.6 µs
• basic_regex: 39.8 µs
• multi_pattern_hit: 21.8 µs
• perl_regex: 128.1 µs
• case_insensitive_hit: 16.8 µs
• word_boundary_hit: 16.4 µs
• extended_regex_hit: 16.3 µs
• extended_regex: 39.5 µs
• scan_1000_lines_regex: 5.5 ms
• scan_1000_lines_fixed: 697.1 µs
• fixed_string_hit: 16.1 µs

---

[codecov]

Codecov Report

❌ Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.48%. Comparing base (2a6a3ab) to head (079619e).

Files with missing lines	Patch %	Lines
src/lib.rs	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #13      +/-   ##
==========================================
- Coverage   95.82%   95.48%   -0.34%     
==========================================
  Files           6        6              
  Lines        1414     1419       +5     
  Branches      140      140              
==========================================
  Hits         1355     1355              
- Misses         58       63       +5     
  Partials        1        1              

Flag	Coverage Δ
macOS_latest	96.30% <16.66%> (-0.35%)	⬇️
ubuntu_latest	96.30% <16.66%> (-0.35%)	⬇️
windows_latest	0.00% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.