fix: avoid retaining resized font chains

[Happypig375]

Summary

• snapshot caller-provided local typefaces once and expose a stable read-only view
• resize painters from the local-only snapshot so repeated FontSize changes no longer feed global faces back into a growing Fonts chain
• exercise repeated same-painter local-face and size switching in the reproducible profiler from perf: add reproducible font startup profiler #317
• cover single-use enumerables, defensive snapshots, stable face order/count, repeated resizing and switching, and a real Comic Neue custom face

Validation

• Release builds passed for Rendering.Tests and Rendering.Benchmarks
• CSharpMath.Rendering.Tests.TestFonts: 5 passed
• low-iteration font-profile smoke: 10 scenarios, no errors
• both switching scenarios exercised the same MathPainter across all four faces and reported retained-after-GC evidence
• scoped format checks and git diff checks passed

This is stacked on #317 because it extends that profiler. It addresses the unbounded resize/switching retention component of #107; deeper extraction of renderer-ready bundled-font data remains separated under #191.

Progress on #107