fix(rtbtool): fix arg-parsing bugs and converge CLI with mvtbtool

[petercorke]

Summary

• Fixes two real argparse bugs in rtbtool: ArgumentParser("Robotics Toolbox shell") was setting prog instead of description, and --confirmexit/-x lacked action="store_true" so it demanded a value argument instead of behaving as a flag.
• Converges rtbtool's CLI with MVTB's mvtbtool (the more deliberately-designed sibling tool): adds a shared _bintools.py (line-wrapping/defaults help formatter, RTB_LINK), an RTB_OPTIONS env var for default options (mirrors MVTB_OPTIONS), and resolves short-flag collisions between the two tools (-r meant --resultprefix here but --run in mvtbtool; -b meant --no-banner here but --base in mvtbtool — --theme/-t and --prompt/-P also realigned to match).
• Replaces the sys.argv mutation trick with explicitly passing argv= to IPython.start_ipython, matching mvtbtool's approach.
• Adds tests/test_bin.py smoke tests (--help, startup-to-prompt via closed stdin, script execution, RTB_OPTIONS), mirroring MVTB's tests/test_bin.py. rtbtool previously had zero test coverage.

Test plan

• rtbtool --help renders correctly with wrapped help text and defaults
• pytest tests/test_bin.py -v — 5/5 passing
• Manually verified --book, --theme, --resultprefix, --showassign, RTB_OPTIONS all still work
• ruff check/ruff format clean on new/changed code (pre-existing lint debt in the star-import section left untouched, out of scope)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 0% with 44 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (298f4c0) to head (00f758f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/roboticstoolbox/bin/_bintools.py	0.00%	23 Missing ⚠️
src/roboticstoolbox/bin/rtbtool.py	0.00%	21 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #557   +/-   ##
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  Coverage   0.00%   0.00%           
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  Files        141     142    +1     
  Lines      13659   13694   +35     
=====================================
- Misses     13659   13694   +35     

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