Add configurable hyphen boundary limits

[vanderlee]

What changed

• Add runtime setters and getters for minimum characters before and after a hyphenation point.
• Allow passing null to restore the active language's defaults.
• Apply overrides after loading language/cache data, keeping generated caches language-specific and reusable.
• Add regression coverage and regenerate the API documentation.

Why

The engine already reads left_min_hyphen and right_min_hyphen from language data, but applications cannot override those limits without editing generated cache files. This also provides the requested control over how many characters remain after a line break.

Closes #35.
Closes #81.