Add Script/Subcommand to fetch calibration data file updates

[kmgill]

Method A: Script/Subcommand would

• fetch current caldata.toml from GitHub
• Fetch referenced files if not already present
• Write files to ~/.marsdata

Method B: Fetch via git clone/pull. Requires: git.

Needs to support running on Linux/macos/Windows. Duplicating a script in both Bash and PowerShell is out.

[kmgill]

Subcommand added to MRU as update-cal-data

• Option -n | --noreplace prevents replacing existing files
• Option -l | --local-store overrides the default calibration file storage directory

[kmgill]

Completed