Optimize nth and nth_back for BoundTupleIterator

[Owen-CH-Leung]

See #4787

This PR optimizes nth and nth_back for BoundTupleIterator, and added unittest & benchmarks for these 2 APIs. Here are the benchmark of the optimized nth and nth_back:

On Stable toolchain

With Optimization

tuple_nth               time:   [283.96 ns 286.42 ns 291.01 ns]
tuple_nth_back          time:   [288.92 ns 289.83 ns 291.15 ns]

The default nth and nth_back implementation

tuple_nth               time:   [2.0933 µs 2.0961 µs 2.0992 µs]
tuple_nth_back          time:   [2.0425 µs 2.0445 µs 2.0468 µs]

On nightly toolchain

With Optimization

tuple_nth               time:   [275.54 ns 275.97 ns 276.49 ns]
tuple_nth_back          time:   [315.25 ns 343.92 ns 375.81 ns]

The default nth and nth_back implementation

tuple_nth               time:   [1.9814 µs 1.9846 µs 1.9883 µs]
tuple_nth_back          time:   [2.0314 µs 2.0705 µs 2.1266 µs]

[Icxolu]

Thank you very much, just some small comments.

[codspeed-hq]

CodSpeed Performance Report

Merging #4897 will degrade performances by 12.82%

_{Comparing Owen-CH-Leung:optimize_nth_and_nthback_for_boundtupleiter (7ac2f20) with main (2c732a7)}

🎉 Hooray! codspeed-rust just leveled up to 2.7.2!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

Summary

❌ 1 regressions
✅ 85 untouched benchmarks
🆕 2 new benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	extract_float_downcast_fail	396.7 ns	455 ns	-12.82%
🆕	tuple_nth	N/A	4.3 µs	N/A
🆕	tuple_nth_back	N/A	4.3 µs	N/A

[Icxolu]

LGTM, thanks 🚀