shred: two refactorings

[cakebaker]

This PR applies two refactorings:

• it removes create_compatible_sequence which simply delegates to create_test_compatible_sequence and calls this function instead
• it changes the type of the random_source param of create_test_compatible_sequence from Option<&RefCell<File>> to &RefCell<File> as the function is never called with None

[codspeed-hq]

Merging this PR will improve performance by 4.73%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
✅ 321 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	ls_recursive_balanced_tree[(6, 4, 15)]	52.3 ms	49.6 ms	+5.5%
⚡	Simulation	ls_recursive_wide_tree[(10000, 1000)]	34.3 ms	33 ms	+3.96%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing cakebaker:shred_remove_fn (ec33bb8) with main (7a944ce)}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/io-errors (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/retry (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/dd/no-allocate is now passing!