fix: scientific notation is incorrectly parsed in general numeric sort

[Kaua-Klassmann]

Description

This PR fixes the general numeric sort to parse correctly scientific notations with sign

Changes

• Change "peek_nth(2)" to "peek_nth(1)" on get_leading_gen
• Add "exponents-positive-general" test to validate general numeric sort

Fixes #10317

[codspeed-hq]

Merging this PR will degrade performance by 7.32%

❌ 1 regressed benchmark
✅ 283 untouched benchmarks
⏩ 38 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	sort_general_numeric[200000]	660.8 ms	712.9 ms	-7.32%

---

_{Comparing Kaua-Klassmann:fix_scientific_notation_is_incorrectly_parsed_in_general_sort (33f9585) with main (ec7e81e)}

Footnotes

1. 38 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:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[sylvestre]

i am not a fan of this test (and the fixtures/sort files)
please test this way:
printf '1\n1e-5' | sort -g

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)

[ChrisDryden]

I don't think I would be too worried about the performance regression here since the benchmark was only 1 digit scientific notation numbers anyways so the entire benchmark wasn't even going in this code path before

[ChrisDryden]

Just waiting on the CI