Improve usability with configurable fonts, symbol search, and bug fixes

[AbhiAgnal]

Summary

This PR contains several usability improvements and bug fixes for Ripes.

Improvements

• Add search/filter support to the Symbol Navigator.
• Add configurable fonts for:
  • Source editor
  • Executable code view
  • Register pane
• Persist register display radix across sessions.
• Generate a proper macOS application icon during the build.
• Improve processor diagram readability.

Bug fixes

• Fix executable code disassembly showing unknown instructions by decoding from the loaded memory image.
• Fix save dialog source filename extension handling when the user already provides an extension.

Tested

• macOS (Apple Silicon)
• Qt 6

[mortbopet]

Thanks for the PR - a few comments.