fix(widgets): preserve fractional scale bar distances

[premsinghsodha7]

Fixes #233.

ScaleBar truncates kilometre and mile labels to integers: 1,900 m is labelled 1 km, and 3,200 m is labelled 1 mi instead of about 1.99 miles. Preserve fractional values using the locale decimal separator and at most two decimal places. Whole metres and feet keep their existing formatting; exactly 1,000 m now uses 1 km. No new dependencies or public API changes.

Validation:

• Four of five new JVM regression tests fail with the extracted original logic; all five pass with the fix.
• Widget unit tests and module lint passed; widget lint XML contains no issues.
• Demo app and instrumentation APK builds passed.
• Two rendering tests passed on Pixel_9_Pro_API_35, Android 15/API 35, 480 dpi. They compose the actual ScaleBar with a controlled projection and assert 1.98 km and 1.23 mi are displayed on light and dark backgrounds. Both captured widget images were visually inspected.
• Updated live-map tests for fractional labels and corrected their reference screen coordinates to use horizontal width. All three explicitly skipped with Maps API key not specified; live map tiles/projection integration remains unverified.
• :maps-app:lintDebug, spotlessCheck, and git diff --check passed.

The device rendering tests use a mocked projection and need no API key. Production drawing and projection calculation are unchanged.

• Existing issue discusses the bug (ScaleBar has up to 100% error #233).
• Tests and module linter pass.
• Code coverage report not run.
• No public API documentation changes needed.

Created as a draft per repository guidance for review of the label-precision approach.