internal: try use new PyLong API for num-bigint feature

[chirizxc]

Related: #6040

See codspeed comment for benchmark improvements.

[codspeed-hq]

Merging this PR will improve performance by 36.99%

⚠️ 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

⚡ 4 improved benchmarks
✅ 122 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	extract_bigint_huge_negative	12.9 µs	8.5 µs	+52.56%
⚡	extract_bigint_small	2.6 µs	1.8 µs	+44.86%
⚡	extract_bigint_huge_positive	11.7 µs	8.5 µs	+38.01%
⚡	extract_bigint_big_negative	3.9 µs	3.4 µs	+15.47%

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.

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_{Comparing chirizxc:PyLongForBigInt (05b34ba) with main (771558e)}