Fix Arraypool rent without try/finally block

[alinpahontu2912]

No description provided.

[Copilot]

Pull request overview

This PR hardens System.Formats.Tar against ArrayPool<byte> buffer leaks by ensuring all rented arrays are returned via try/finally, even when an exception occurs during stream I/O or header processing.

Changes:

• Wrap ArrayPool<byte>.Shared.Rent(...) usages in try/finally in writer paths so buffers are always returned.
• Wrap ArrayPool<byte>.Shared.Rent(...) usages in try/finally in reader paths and stream-advancing/copy helpers to prevent leaks on read failures.
• Ensure temporary pooled buffers used for padding / metadata generation are returned on all exit paths.

Reviewed changes

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

File	Description
src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarWriter.cs	Ensures pooled buffers used during async entry writes and final record writes are always returned.
src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHelpers.cs	Ensures pooled buffers in stream advance/copy helpers are always returned, even on read/write failures.
src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHeader.Write.cs	Ensures pooled buffers for async padding writes and extended-attribute stream generation are always returned.
src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHeader.Read.cs	Ensures pooled buffers used while reading headers and metadata blocks are always returned on all paths.

[gfoidl]

Is this needed with Unsafe code best practices in mind?