Feature/issue 2630v2

[AndreiGorelov]

Issues

Fixes #2630

Proposed changes

This PR fixes incorrect rendering of tuplet labels when importing MusicXML files.
Root cause: MusicXmlImporter parsed for note duration correctly, but completely ignored the element inside. As a result, the show-number and bracket attributes were never read, and LineBarRenderer had no way to distinguish between tuplets that should display a label and those that should not.

• Added TupletShowNumber enum (Actual/Both/None ) representing the three states of the MusicXML show-number attribute
• Added showTupletNumber: TupletShowNumber and showTupletBracket: boolean fields to Beat, both defaulting to safe backward-compatible values
• Updated MusicXmlImporter._parseNotations() and added MusicXmlImporter._parseTupletVisibility to read and store show-number and bracket on the corresponding beat
• Replaced the hardcoded num:den lookup table in LineBarRenderer._paintTupletHelper with an algorithmic natural-denominator rule.

Example fixed cases:

• 6:9 (nested duplet in compound time) now correctly shows 6 instead of 6:9
• Compound nested ratios like 12:27 with show-number="none" bracket="no" are now fully suppressed instead of rendering a phantom 12:27 label

Checklist

• I consent that this change becomes part of alphaTab under it's current or any future open source license
• Changes are implemented
• New tests were added

Some reference images for current tests need to be updated.

Further details

• This is a breaking change
• This change will require update of the documentation/website

[Danielku15]

Fixed as part of #2650