uutils AWK progress report

I will be updating this issue as we make progress. Please feel free to take down good first issues here and in the issue tracker.

Interpreter Tasklist

• for-each loops. May be complicated to get right due to the configurable order, so I'm putting it off a bit.
• Field splitting mode of FIELDWIDTHS.
• Some other record splitting modes.
• Support for getline and print/print redirections in the VM.
• General I/O in the event loop and VM dispatch.
• Wire in lexer/parser in the interpreter for robust indirect call parsing + built-in funs disambiguation, libloaded funs disambiguation.
• Remaining built-in vars auto-setting.
• Magic around SYMTAB, FUNCTAB, PROCINFO. I'm handling this.
• Range patterns. Requires either allocating a register for the duration of the program or doing so as an internal symbol in the symbol table.
• Etc.

Various

• One or two parser differentials I've got written down and should get to fixing. God I hate AWK's grammar. It would be neat to refactor/rewrite the parser into using chumsky combinators.
• More robust --pretty-printing, with more precedence disambiguation and default args expansion for built-in functions.
• Fully wire in compatibility modes and ensure they are enforced.
• Library loading (via libloading) and C/FFI function calls.
• Debugger.
• Get clap to behave properly.
• Sanity.

The issue names no files, tests, or single entry point. Choose one unchecked item from the Interpreter Tasklist, then trace the relevant interpreter, VM, event-loop, lexer, or parser area named in the task. Done requires completing that narrowly selected item and verifying its behavior against the project's existing checks.