Add multi-threading for pack/unpack

[cr3ativ3cod3r]

Description

This PR introduces parallel processing of pack and unpack operations. Previously the layers were packed and unpacked sequentially.

• In savekitfilelayers, calls to savecontentlayer is now executed in a new goroutine. They are also indexed, so that the order of layers is preserved.
• In unpackrecursive, calls to unpacklayers is now executed in a new goroutine.
• For the progress bars, created an instance of mpb.Progress and each goroutine adds a bar to this shared instance.
• In ignorepaths struct, added a mutex and used it in matches method as MatchesOrParentMatches is not safe for concurrent access.

Linked issues

closes #254

AI-Assisted Code

• This PR contains AI-generated code that I have reviewed and tested
• I take full responsibility for all code in this PR, regardless of how it was created

[gorkem]

Some critical issues to address and also missing

• Race detector tests (go test -race)
• Concurrent layer ordering tests
• Performance benchmarks

[gorkem]

saveContentLayer -> packLayerToTar -> writeLayerToTar
writeLayerToTar calls ignore.Matches` for each file With the mutex, all file traversal becomes serialized. Parallel implementation may be SLOWER than sequential due to lock contention.

[gorkem]

This is introducing concurrent writes to shared Kitfile fields without synchronization, causing potential data races and corruption. The same pattern is repeated on other layers too.

[gorkem]

This closes the results channel and returns. However, some goroutines might still be running and will panic when trying to send to the closed channel.