Fixes

• Fixed
  • remove invalid arg
• Changed
  • remove unused cache refresh tracking

Remove slowdown from xonsh v18

• Changed
  • drop trying to find a binary in a nonexistent cache, which is now very costly, especially with larger $PATHs

Fully rename to mise

• Changed
  • renamed rtx.py to mise.py to avoid issues in loading

Rename rtx to mise

Rename project name, binary lookup, environent variables to use mise instead of rtx to match the original project (old environment variables still work, and old binary is still searched for as a backup)