feat!: partial rewrite

[peter-bread]

Instead of this being a weird binary wrapper around a shell script, rewrote the core functionality in Go.

Breaking Changes:

Removed yq dependency

• since the core logic is now written in Go, we can use a go package for the yaml handling.

gam script removed

• no longer needed. Its functionality has now been split into 2 commands

gam run added

• this command runs the account switching logic

gam hook added

• this prints a script to be sourced to hook into the shell's cd command