Fix inline math rendering in markdown by using Text.rich instead of SingleChildScrollView

[frdteknikelektro]

Problem

Inline math expressions wrapped in SingleChildScrollView cause unwanted line breaks in markdown text. The opaque widget breaks flutter_markdown_plus's text merging chain, forcing each adjacent text segment into its own full-width RichText.

Solution

Differentiate rendering based on math style:

• Display math (block): Keep SingleChildScrollView for horizontal scrolling of large expressions
• Inline math: Use Text.rich with WidgetSpan so flutter_markdown_plus can merge it with adjacent text spans into a single RichText

Result: inline math now flows naturally with surrounding text without line breaks.

Changes

• Split rendering logic into two paths based on MathStyle
• Inline math returns Text.rich(TextSpan with WidgetSpan child)
• Display math retains original SingleChildScrollView behavior
• Added comments explaining the inline math approach

[frdteknikelektro]

@gazreese Maybe you could take a look