fix: preload fallback fonts on await draw and fix mesh '?' width

[mlightcad]

Summary

• When awaitFonts is enabled, MText/Shape.asyncDraw also requests default/symbol fallback fonts from getFontsToLoad(), so single-pass draws can resolve glyphs like diameter (U+2205 → amgdt) without relying on a later fontLoaded redraw.
• MeshFont.getNotFoundTextShape now goes through getCharShape('?') so the glyph is loaded before measuring advance width, preventing zero-width placeholders that overlap the next character.
• Bump @mlightcad/mtext-renderer to 0.12.4 and add regression coverage for both behaviors.

Test plan

• Run packages/mtext-renderer vitest suite (including meshFont.notFound and render-remote-font-loading)
• With awaitFontsBeforeDraw / awaitFonts: true, draw MText containing U+2205 and confirm diameter resolves on the first pass
• Confirm a missing mesh glyph shows ? with non-zero advance and no overlap with the following character
• Confirm fire-and-forget lazy draws (awaitFonts: false) still only request content/style fonts