feat: add historic git-backed filesystem

[dmcilvaney]

When creating synthetic dist-gits, there are certain packages that use overlays which mutate the calculated release value for a package. If the overlays are only applied to the last commit in the dist-git, then if a package changes the 'version' of a package the autorelease tool will see the version change ONLY on that last commit, and conclude the release should be reset back to '1'. If we then add another commit to the dist-git, the version should be '2', but the autorelease tool will still see the version bump happen only on the last commit, and again reset the release to '1'. (see kernel-headers for an example)

To avoid this, we must apply the overlays to all commits in the dist-git, as they would have appeared at the time of the commit. azldev already abstracts filesystem access through 'fs', so we can implement a 'gitfs' that loads toml configs from the project's git history. A copy-on-write in-memory filesystem allows for writing if necessary.

[dmcilvaney]

Requires #216 for tests to pass

[Copilot]

Pull request overview

Adds infrastructure to load project configuration from a repository’s historical git state, enabling “replay” of overlays across all commits when generating synthetic dist-gits.

Changes:

• Introduces internal/utils/gitfs — a read-only afero.Fs backed by a git tree at a specific commit, compatible with existing glob/include behavior.
• Adds historic project-config entry points (LoadProjectConfigAtCommit, ResolveComponentOverlaysAtCommit) that read config from git history using gitfs plus a writable in-memory overlay.
• Extends fileperms with read-only permission constants used by the synthetic/historic filesystem view.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
internal/utils/gitfs/gitfs.go	Implements the git-backed read-only afero.Fs used to read files at a specific commit.
internal/utils/gitfs/gitfs_test.go	Validates reading, stat, readdir, doublestar globbing, and read-only behavior for gitfs.
internal/utils/fileperms/fileperms.go	Adds ReadOnlyFile / ReadOnlyExec modes for immutable filesystem views.
internal/projectconfig/historic.go	Adds APIs to load and resolve project config/overlays at a specific commit using gitfs.
internal/projectconfig/historic_test.go	Tests historic config loading and overlay resolution across commits and permissive parsing behavior.