Mix instance type into generated hashes

[00200200]

Summary

Generated __hash__ mixed in a class identity captured when the method was created.
Undecorated subclasses therefore inherited the base class's hash component and collided for equal field values (#528).

This switches that component to id(type(self)), so each subclass hashes distinctly while same-class instances keep matching hashes. That matches the hashing docs and Hynek's note on mixing a type identity into the hash.

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Fixes #528

[codspeed]

Merging this PR will degrade performance by 14.66%

⚠️ 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

❌ 1 regressed benchmark
✅ 16 untouched benchmarks
⏩ 2 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	test_hash	2.7 ms	3.1 ms	-14.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing 00200200:fix-528-hash-instance-type (cfc1c25) with main (65c80d7)²}

Footnotes

1. 2 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. ↩

2. No successful run was found on main (8f76777) during the generation of this report, so 65c80d7 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩