Add periodic progress reporting during heap enumeration

[Copilot]

verifyheap and dumpheap -stat walk the entire managed heap with zero output, making large-dump analysis (e.g. 19 GB / 248M objects) indistinguishable from a hang for minutes at a time.

Changes

• ProgressReporter.cs (new) — Time-gated helper that fires a callback at most once per interval and exposes FormatProgressMessage(scanned, total) for consistent output formatting.
• HeapWithFilters.cs — Added ProgressCallback: Action<long, long> property. When set, EnumerateFilteredObjects() materializes segments in a single pass to compute total heap bytes, then invokes the reporter per valid object.
• VerifyHeapCommand.cs / DumpHeapCommand.cs — Wire up the progress callback; dumpheap only enables it under -stat (the silent-walk case).
• Microsoft.Diagnostics.ExtensionCommands.csproj — Added InternalsVisibleTo for the new unit test project.
• Microsoft.Diagnostics.ExtensionCommands.UnitTests (new) — Unit tests for ProgressReporter covering interval gating, byte accumulation, and message formatting.

Example output

> dumpheap -stat
Scanning heap: 3,200 MB / 16,300 MB (20%)...
Scanning heap: 6,500 MB / 16,300 MB (40%)...
Scanning heap: 9,800 MB / 16,300 MB (60%)...
...
Statistics:

Progress lines emit every ~10 seconds via Console.WriteLine. Commands that already stream output continuously (dumpheap without -stat, finalizequeue, gchandles) are unaffected.

Warning

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• securitytools.pkgs.visualstudio.com
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Original prompt

Check if I have permissions to push commits to PR #5763 in dotnet/diagnostics. The PR is from danmoseley's fork (danmoseley/diagnostics, branch heap-progress) and has maintainer_can_modify set to true. Try to determine if the current user (hoyosjs) has write access to the base repository dotnet/diagnostics.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Can you push commits to this PR?

Assistant: Yes, you should be able to push commits to this PR. Here's why:

1. maintainer_can_modify is true — The PR author (@danmoseley) enabled "Allow edits from maintainers" when creating this PR from their fork (danmoseley/diagnostics → dotnet/diagnostics).

2. You have write access — As long as you have push/write permissions to the base repository (dotnet/diagnostics), GitHub allows you to push commits directly to the PR's head branch (heap-progress on danmoseley/diagnostics).

You can push to the branch by adding the fork as a remote and pushing to the heap-progress branch:

git remote add danmoseley https://github.com/danmoseley/diagnostics.git
git push danmoseley HEAD:heap-progress

This is documented in GitHub's guide on Committing changes to a pull request branch created from a fork.

User: Do you have permissions to modify this PR?

Assistant: I'm waiting for your confirmation to proceed with the tool call that was just proposed.

This pull request was created from Copilot chat.

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