Add tar tests for >8GB file entries using simulated streams

[Copilot]

Description

Adds automated tests for tar archives with >8GB file entries using SimulatedDataStream and ConnectedStreams to avoid materializing large data. Previous manual tests required actual disk space and were unsuitable for CI.

Tests use parallel writer/reader pattern where:

• Writer task streams tar data via SimulatedDataStream (generates dummy data pattern without allocation)
• Reader task consumes via ConnectedStreams.CreateUnidirectional() (in-memory pipe with bounded buffer)
• No intermediate storage required, data flows directly between writer and reader

Covers PAX and GNU formats at LegacyMaxFileSize + 1 (8GB + 1) testing both sync and async APIs.

Customer Impact

N/A - test infrastructure only. Enables CI validation of >8GB tar entry handling without resource constraints.

Regression

No - this adds test coverage for existing functionality fixed in PR #88280.

Testing

8 tests added (4 scenarios × 2 sync/async variants), all passing in ~68 seconds with no disk/memory overhead.

Risk

Very low - test-only changes with no production code modifications. Added dependencies (ArrayBuffer, MultiArrayBuffer, StreamBuffer) are existing, stable utilities used by ConnectedStreams.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add tar test with custom stream that simulates reading/writing >8GB file entry</issue_title>
<issue_description>Follow up of PR #88280 and specifically, follow-up of this commit: 5482008

Need to create a test that actually runs in the CI that simulates writing and reading the long data section, but without torturing our CI machines' disk and memory.</issue_description>

<agent_instructions>Consider using src/libraries/System.Formats.Tar/tests/SimulatedDataStream.cs to simulate the large entry, ideally, write the code in such a way that does not require storing the entire tar archive on disk or in memory.

One thing that can help here is the ConnectedStreams test utility and run the writing and reading part in parallel.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@ Tagging subscribers to this area: @dotnet/area-system-formats-tar See info in [area-owners.md](https://github.com/dotnet/runtime/blob/main/docs/area-owners.md) if you want to be subscribed.

Issue Details

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Follow up of PR #88280 and specifically, follow-up of this commit: 5482008

Need to create a test that actually runs in the CI that simulates writing and reading the long data section, but without torturing our CI machines' disk and memory.

Author:	carlossanlop
Assignees:	-
Labels:	test-enhancement, area-System.Formats.Tar
Milestone:	Future

• Fixes Add tar test with custom stream that simulates reading/writing >8GB file entry #89037

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[rzikm]

@copilot The two tests look almost identical, can you deduplicate them using additional isAsync paramter?

[rzikm]

@copilot can you try again?

[Copilot]

Pull request overview

This PR adds automated test coverage for tar archives containing file entries larger than 8GB, addressing a gap identified in PR #88280. The tests use SimulatedDataStream and ConnectedStreams to validate large file handling without requiring significant disk space or memory resources.

Changes:

• Adds comprehensive test class with parallel writer/reader pattern for testing >8GB tar entries
• Tests cover PAX and GNU formats (which support unlimited file sizes) with both sync and async APIs
• Includes necessary dependencies for ConnectedStreams infrastructure in project file

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
TarWriter.WriteEntry.LargeFiles.Tests.cs	New test class implementing parallel streaming tests for large file entries using simulated streams
System.Formats.Tar.Tests.csproj	Adds references to ConnectedStreams and supporting buffer utilities (ArrayBuffer, MultiArrayBuffer, StreamBuffer)

[rzikm]

@copilot address code review comments

[rzikm]

/ba-g failing test is #123216