www/py-nicegui{,-nogui}: Update 2.5.0 => 2.15.0

• Add devel/py-python-engineio dependency.
• Add www/py-starlette dependency.
• Make www/py-libsass dependency optional.
• Add REDIS option.

Changelogs:
https://github.com/zauberzeug/nicegui/releases/tag/v2.7.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.8.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.8.1
https://github.com/zauberzeug/nicegui/releases/tag/v2.9.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.9.1
https://github.com/zauberzeug/nicegui/releases/tag/v2.10.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.10.1
https://github.com/zauberzeug/nicegui/releases/tag/v2.11.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.11.1
https://github.com/zauberzeug/nicegui/releases/tag/v2.12.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.12.1
https://github.com/zauberzeug/nicegui/releases/tag/v2.13.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.14.0
https://github.com/zauberzeug/nicegui/releases/tag/v2.14.1
https://github.com/zauberzeug/nicegui/releases/tag/v2.15.0

PR: 286247