refactor(build): optimize allocations and add tests

[Jguer]

introduces performance optimizations and adds test coverage to the build package.

• pre-allocated maps and slices in installer.go and pkg_archive.go to reduce memory allocations.
• used strings.builder in errors.go for more efficient error string construction.
• tests for the parsepackagelist function.

[Copilot]

Pull Request Overview

This pull request refactors parts of the build package to optimize memory allocations and improve error construction performance, while also adding test coverage for the parsePackageList function.

• Optimized map and slice pre-allocation in installer.go and pkg_archive.go
• Refactored error string construction in errors.go using strings.Builder
• Added comprehensive tests for the parsePackageList function in pkg_archive_test.go

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/sync/build/pkg_archive_test.go	Added various test cases covering different package list parsing scenarios
pkg/sync/build/pkg_archive.go	Optimized the allocation of the pkgdests map by pre-sizing based on the line count
pkg/sync/build/installer.go	Improved pre-allocation for maps and slices to reduce memory allocations
pkg/sync/build/errors.go	Refactored error message generation from concatenation to use strings.Builder