feat(labels): implement vertical barrier label

[ngriffiths13]

This PR implements a function that calculates a vertical barrier label using a timedelta strategy.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 94.00%. Comparing base (89199a9) to head (d0f8afb). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
polars_trading/labels/dynamic_labels.py	75.00%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #9 +/- ## ========================================== - Coverage 96.92% 94.00% -2.93% ========================================== Files 6 6 Lines 130 150 +20 ========================================== + Hits 126 141 +15 - Misses 4 9 +5 ```

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[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #9 will not alter performance

_{Comparing feat/vertical-barrier (d0f8afb) with main (89199a9)}

Summary

✅ 10 untouched benchmarks

🆕 1 new benchmarks

Benchmarks breakdown

	Benchmark	main	feat/vertical-barrier	Change
🆕	test__get_vertical_barrier_by_timedelta__benchmark[trade_data0]	N/A	37.3 ms	N/A