Fixing validation issues and tag injection

[sn]

This pull request introduces stricter validation for HTML tag names, CSS property names, and theme token names/values to prevent injection vulnerabilities and malformed output in NitroUI. The changes add regular expression-based validation and raise clear errors for invalid input throughout the element, style, stylesheet, and theme modules.

Security and Validation Improvements

• HTML tag names are now validated in the tag setter of Element, ensuring they start with a letter and only contain letters, digits, and hyphens.
• CSS property names are validated using a shared regular expression in both CSSStyle and the stylesheet renderer, blocking unsafe identifiers and injection vectors. [1] [2] [3] [4] [5] [6]
• Theme token names and values are validated in Theme.get_css_variables() to ensure only safe identifiers and values are used for CSS custom properties. [1] [2]

Other Changes

• The package version is bumped from 1.0.10 to 1.0.11.