Close writable entry streams during async archive disposal

[Copilot]

SaveToAsync on writable archives completed without releasing tracked entry streams on async disposal, leaving output files/directories locked. The sync path already closed these streams; the async path now matches that behavior.

• Core fix (shared writable archive disposal path)

  • Added DisposeAsync override in AbstractWritableArchive.Async to close tracked writable entries (newEntries, removedEntries, modifiedEntries) after base.DisposeAsync().

• Coverage across writable archive types

  • Added focused async regression tests for:
    • TarArchive
    • ZipArchive
    • GZipArchive
  • Each test adds an entry with closeStream: true, calls SaveToAsync, disposes asynchronously, and asserts the source stream is disposed.

• Behavioral parity (sync vs async)

  • Async disposal now performs the same entry-stream cleanup already present in sync Dispose(), preventing lingering file handles after async save flows.

public override async ValueTask DisposeAsync()
{
    await base.DisposeAsync().ConfigureAwait(false);
    newEntries.Cast<Entry>().ForEach(x => x.Close());
    removedEntries.Cast<Entry>().ForEach(x => x.Close());
    modifiedEntries.Cast<Entry>().ForEach(x => x.Close());
}

[Copilot]

Pull request overview

This PR fixes async disposal for writable archives so entry streams tracked during async save flows are closed like the synchronous disposal path.

Changes:

• Adds DisposeAsync cleanup in AbstractWritableArchive for new, removed, and modified writable entries.
• Adds async regression tests for Zip, Tar, and GZip writable archives to verify closeStream: true entry streams are disposed.

Reviewed changes

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

File	Description
src/SharpCompress/Archives/AbstractWritableArchive.Async.cs	Adds async disposal cleanup for tracked writable archive entries.
tests/SharpCompress.Test/Zip/ZipArchiveAsyncTests.cs	Adds Zip async disposal regression coverage.
tests/SharpCompress.Test/Tar/TarArchiveAsyncTests.cs	Adds Tar async disposal regression coverage.
tests/SharpCompress.Test/GZip/GZipArchiveAsyncTests.cs	Adds GZip async disposal regression coverage.

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