Fix dehumanize to handle decimal fractions

[rstar327]

Pull Request Checklist

• 🧪 Added tests for changed code.
• 🛠️ All tests pass when run locally (run tox or make test to find out!).
• 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• 📚 Updated documentation for changed code.
• ⏩ Code is up-to-date with the master branch.

Description of Changes

Closes: #1237

dehumanize() currently only matches integer values in time strings, so inputs like "3.5 hours ago" are parsed incorrectly — the decimal portion is silently ignored, treating 3.5 as 3.

This PR updates the number matching regex to support decimal fractions using either . or , as the decimal separator, and parses values as float instead of int:

# Before
num_pattern = re.compile(r"\d+")
change_value = int(num_match.group())

# After
num_pattern = re.compile(r"\d+(?:[.,]\d+)?")
change_value = float(num_match.group().replace(",", "."))

Example:

>>> arrow.get("2025-12-10T09:00:00").dehumanize("2 days 3.5 hours ago")
# Before: <Arrow [2025-12-08T06:00:00+00:00]>  (3.5 truncated to 3)
# After:  <Arrow [2025-12-08T05:30:00+00:00]>  (correct)

Tests added:

• Decimal hours (. separator)
• Decimal with multiple units ("2 days 3.5 hours ago")
• Comma decimal separator ("3,5 hours ago")
• Decimal in future strings ("in 1.5 hours")
• Decimal minutes
• Integer values still work correctly

All 1909 tests pass with 99.93% coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b423717) to head (24e45be).

Additional details and impacted files

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  Files           10        10           
  Lines         2315      2315           
  Branches       358       358           
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  Hits          2315      2315           

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