docs: add BitStr zero-copy view to README, bump to 0.4.3

[jcfangc]

• Add type comparison table (BitString / BitStr — like String / &str)
• Extend feature list with zero-copy view, conversion, comparison & hashing
• Expand example to demonstrate BitStr slicing, matching, comparison, and to_bit_string() roundtrip
• Bump version to 0.4.3

[codecov-commenter]

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[codspeed-hq]

Merging this PR will not alter performance

⚡ 2 improved benchmarks
❌ 3 regressed benchmarks
✅ 166 untouched benchmarks
⏩ 11 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	count_ones/len_65/alternating/bit_string	248.6 ns	277.8 ns	-10.5%
❌	count_ones/len_65/dense/bit_string	248.6 ns	277.8 ns	-10.5%
❌	count_ones/len_65/sparse/bit_string	248.6 ns	277.8 ns	-10.5%
⚡	matches_at/len_65/no/unaligned/bit_string	434.2 ns	375.8 ns	+15.52%
⚡	matches_at/len_65/yes/unaligned/bit_string	434.2 ns	375.8 ns	+15.52%

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 feat/release-docs (49d73e8) with main (c89f04f)}

Footnotes

1. 11 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. ↩