Fix ZipArchive Update mode rewriting unchanged archives on Dispose

[alinpahontu2912]

Fix ZipArchive in Update mode rewriting when no changes made

Opening an entry stream in ZipArchiveMode.Update would immediately mark the archive as modified, causing Dispose to attempt a rewrite even when no actual writes occurred. This threw NotSupportedException on non-expandable streams like fixed-size MemoryStream.

The fix tracks actual writes via WrappedStream and only marks the entry as modified when data is written. Archives created on empty streams are marked as new to ensure they're still written on first creation.

Fixes #123419

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[Copilot]

Pull request overview

Fixes a regression where opening entry streams in ZipArchiveMode.Update could mark the archive as modified even when no data was written, causing unnecessary rewrites on Dispose (and failures on non-expandable streams).

Changes:

• Track actual writes in Update mode by notifying the entry only on the first write to the opened stream.
• Skip rewriting Update-mode archives on Dispose unless the archive is actually modified (while still writing newly-created empty archives).
• Add regression tests covering Package/Zip scenarios where entries are read without writes.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/libraries/System.IO.Packaging/tests/Tests.cs	Adds regression test ensuring Package.Open(ReadWrite) doesn’t throw on Dispose when only reading.
src/libraries/System.IO.Compression/tests/ZipArchive/zip_UpdateTests.cs	Updates/extends Update-mode tests and adds regression tests for non-expandable streams.
src/libraries/System.IO.Compression/src/System/IO/Compression/ZipCustomStreams.cs	Adds write-notification plumbing to mark entries modified only when written.
src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.cs	Stops marking entries modified on open; introduces MarkAsModified; adjusts write path to reuse original compressed bytes if unchanged.
src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.Async.cs	Async equivalents of Update-mode changes and unchanged-data handling.
src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchive.cs	Adds Update-mode “write only if modified” behavior and “new archive” detection.
src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchive.Async.cs	Async equivalents of Update-mode “write only if modified” and “new archive” detection.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

[rzikm]

LGTM