feat: add support for tuning alterations

[kulek1]

Note

AI-authored disclosure (alphatab-ai-authored-v1)

Portions of this content were authored by an AI agent. The agent has read
AGENTS.md and the human submitter accepts responsibility for
compliance with the rules in that document.

Issues

Fixes #2802

Proposed changes

This PR adds optional per-string tuning accidental preferences so alphaTab can preserve and render explicit sharp/flat choices such as F# and Gb.

• Adds optional TuningAccidentalMode[] support to the tuning model.
• Preserves tuning accidental preferences through alphaTex, Guitar Pro/GPIF, MusicXML, JSON, and exporters where supported by the format.
• Updates score-info and inline tuning rendering to use each string’s preference.
• Keeps existing behavior unchanged when no accidental mode is specified.
• Replaces an unsafe renderer argument spread with bounded iteration to prevent malformed GPIF tuning data from causing renderer exceptions.
• Adds importer, exporter, model, and visual regression coverage.

Related discussion: alphaTab discussion #2785

Root-cause analysis

Numeric tuning values did not preserve enharmonic spelling, and format-specific sharp/flat metadata was not consistently retained per string.

The renderer also used Math.max(...labels), allowing malformed GPIF tuning data with a large Pitches list to exceed the JavaScript argument limit. The fix preserves optional per-string modes and calculates widths iteratively, while retaining legacy behavior by default.

Checklist

• I consent that this change becomes part of alphaTab under its current or any future open source license
• This PR is linked to an accepted issue (see above)
• Changes are implemented
• New tests were added
• I have read AGENTS.md if an AI helped draft any part of this PR

AI authorship disclosure

• No AI agent authored any part of this PR (description, code, tests, or commit messages)
• An AI agent contributed to this PR. The AI-authored disclosure block
  (alphatab-ai-authored-v1) is present at the top of this body, and I have
  personally reviewed every change and can explain each one

Further details

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