docs: v1.20.0 release prep - DeepCopy documentation and corpus benchmark build tags

[erraggy]

Summary

• Add DeepCopy example and benchmarks to parser package documentation
• Add v1.20.0 benchmark results
• Make corpus benchmarks opt-in via //go:build corpus tag to prevent memory exhaustion

Changes

DeepCopy Documentation

• Add Example_deepCopy() demonstrating how to use DeepCopy for independent document copies
• Add BenchmarkDeepCopy() covering OAS2 and OAS3 documents at various sizes
• Update benchmarks.md with DeepCopy performance metrics

Benchmark Results

• Add benchmarks/benchmark-v1.20.0.txt with complete benchmark results
• Update performance tables in benchmarks.md showing significant improvements:
  • FixParsed: 86μs → 2.3μs (~37x faster)
  • ConvertParsed: 16.2μs → 3.2μs (~5x faster)

Corpus Benchmark Build Tags

• Create corpus_bench_test.go files in parser, validator, differ, fixer packages
• Use //go:build corpus tag to exclude corpus benchmarks from regular runs
• Update Makefile bench-corpus target to use -tags=corpus
• Simplify bench-release target (no longer needs -skip flag)
• Add documentation comment to scripts/backfill-benchmarks.sh

This prevents accidental memory exhaustion when running go test -bench=.

Test plan

• make check passes (2263 tests)
• Corpus benchmarks excluded without -tags=corpus
• Corpus benchmarks run with make bench-corpus or -tags=corpus
• DeepCopy example compiles and runs correctly

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.08%. Comparing base (a1c3cee) to head (6673fb5).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #106   +/-   ##
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  Coverage   75.08%   75.08%           
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  Files          55       55           
  Lines       10040    10040           
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  Hits         7539     7539           
  Misses       1833     1833           
  Partials      668      668           

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[Copilot]

Pull request overview

This PR prepares the v1.20.0 release by adding DeepCopy documentation/benchmarks and making corpus benchmarks opt-in via build tags to prevent memory exhaustion during regular benchmark runs.

Key Changes:

• Adds DeepCopy example and benchmark demonstrating the new code-generated deep copy functionality
• Introduces //go:build corpus tags to exclude resource-intensive corpus benchmarks from default runs
• Documents significant performance improvements from DeepCopy optimization (FixParsed ~37x faster, ConvertParsed ~5x faster)

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
parser/parser_bench_test.go	Adds BenchmarkDeepCopy for OAS2/OAS3 documents at various sizes
parser/example_test.go	Adds Example_deepCopy demonstrating independent document copies
parser/corpus_bench_test.go	New file with corpus benchmarks under //go:build corpus tag
parser/corpus_large_test.go	Removes benchmark, adds migration comment pointing to corpus_bench_test.go
validator/corpus_bench_test.go	New file consolidating corpus validation benchmarks with build tag
validator/corpus_integration_test.go	Removes benchmark, adds migration comment
validator/corpus_large_test.go	Removes benchmark, adds migration comment
fixer/corpus_bench_test.go	New file with corpus fixer benchmark under build tag
fixer/fixer_test.go	Removes benchmark, adds migration comment
differ/corpus_bench_test.go	New file with corpus differ benchmark under build tag
differ/corpus_integration_test.go	Removes benchmark, adds migration comment
Makefile	Simplifies bench-release (removes -skip flag), updates bench-corpus to use -tags=corpus
scripts/backfill-benchmarks.sh	Updates comment explaining corpus benchmarks require -tags=corpus in v1.20.0+
benchmarks/benchmark-v1.20.0.txt	Adds complete v1.20.0 benchmark results including new DeepCopy benchmarks
benchmarks.md	Documents DeepCopy performance, updates FixParsed/ConvertParsed improvements, increases benchmark count to 120+