Add comm utility

[watzon]

This PR implements the comm utility for comparing two sorted files line by line.

Implementation Details

The utility follows the GNU coreutils specification and includes:

Core Features:

• Compare two sorted files and display differences in three columns
• Column 1: Lines unique to file 1
• Column 2: Lines unique to file 2
• Column 3: Lines present in both files

Command Line Options:

• -1: Suppress column 1 (lines unique to FILE1)
• -2: Suppress column 2 (lines unique to FILE2)
• -3: Suppress column 3 (lines that appear in both files)
• --check-order: Check that input files are correctly sorted
• --nocheck-order: Do not check sort order
• --output-delimiter=STRING: Use STRING to separate columns (default: TAB)
• --total: Display a summary with counts for each column
• -z, --zero-terminated: Use NUL as line delimiter instead of newline

Additional Features:

• Support for stdin using - as filename
• Proper error handling with appropriate exit codes
• Full compatibility with BSD comm (macOS) for standard options
• GNU extensions for enhanced functionality

Testing

Comprehensive test suite included covering:

• Basic file comparison
• All column suppression combinations
• Empty file handling
• Stdin support
• Error cases (missing files, wrong number of arguments)
• Custom delimiter functionality

All tests pass and the implementation matches the behavior of GNU coreutils comm.

Progress Update

This brings the project to 75/109 utilities completed (69%). Nice!

[JalonSolov]

Need to format comm_test.v.

Also appears we have a problem with the sort command. :-\

[watzon]

Yeah... the test suite also seems to be very broken on macOS in general