Reduce allocations in Composer, NuGet, Go and Python parsers

[andrew]

Preallocate dependency slices in Composer and NuGet lockfile parsers, and use strings.SplitSeq in Go, Python and Paket parsers to avoid allocating a slice of every line. Preserve empty results, package filtering and deduplication across target frameworks.

Public Parse benchmarks show 26% fewer allocated bytes for the Composer fixture and 5–43% fewer for NuGet fixtures. Synthetic lockfiles with 10,000 dependencies use 43–63% fewer bytes. Line iteration saves another 0.6–1.4% in the six affected line-based formats.

[Copilot]

🟢 Approval recommended

The reviewed changes preserve behavior and have no unresolved blocking issues.

Pull request overview

Reduces allocations in Composer, NuGet, Go, and Python parsers while preserving parsing behavior.

Changes:

• Preallocates Composer and NuGet dependency slices.
• Uses strings.SplitSeq for line-based parsers.
• Adds regression tests and allocation benchmarks.

File summaries

File	Description
lock_capacity_test.go	Adds capacity tests and benchmarks.
line_iteration_test.go	Adds line-ending tests and benchmarks.
internal/pypi/pypi.go	Uses iterator-based line parsing.
internal/nuget/nuget.go	Preallocates dependencies and uses SplitSeq.
internal/golang/golang.go	Uses iterator-based line parsing.
internal/composer/composer.go	Preallocates Composer dependencies.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 0
• Review effort level: Lite

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