fix(gix-traverse): use graph painting for hide() to ensure correct behavior

[Copilot]

The hide() function was lazily traversing hidden commits interleaved with interesting commits during iteration, rather than using proper graph painting. This could potentially include commits that should be hidden if the interesting traversal reached shared ancestors before the hidden traversal painted them.

Changes

• gix-traverse/src/commit/simple.rs: Refactored hide() to fully traverse all hidden tips and mark all reachable commits as Hidden before returning. This matches git's rev-list --not behavior.

• New tests: Added hide_with_graph_painting module with tests for:

  • Hidden tip with longer path to shared ancestor
  • Interesting tip with longer path to shared ancestor
  • Both verify output against git rev-list --not

Graph Painting Approach

Graph:
  A(tip) --> shared
           /
  H(hidden) --> X --> Y --> shared

Before: Hidden traversal interleaved with interesting - shared might be 
        returned before H's longer path marks it hidden.

After:  All commits reachable from H are painted hidden upfront.
        Iteration simply skips any Hidden commits.

Original prompt

In gix-traverse there is a way to hide commits, and all their ancestry. But the implementation isn't correct as it's not based on "graph painting" via gix-revwalk, and can easily include commits in the traversal because they have not yet been seen by the tips that are hiding them.
Add a test, using gix-testtools, completely ignoring the test-suite and style in gix-traverse, to reproduce this issue, and try to fix it.

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[Sebastian Thiel (Byron)]

This is terrible for performance, but it at least fixes the long-standing bug, something that should have been done a while ago.
Still I wonder how this can be implemented incrementally, and fear there is no way… .