feat: replace builtin listeners

[lachlanharrisdev]

Description

The project originally was an INetSim alternative made to be lightweight as a static binary. With the addition of Lua handlers, the codebase was relatively split, having many layers of config, built-in functionality versus programmed, and it become a mess to work with.

This PR removes built-in handlers and instead brings Lua front-and-centre; PCAP(ng) files are now the only file output and are much better supported, config files have been removed in favour of intuitive CLI flag parsing, and docs are now embedded in the binary with clean rendering via go-std-markdown.

Linked Resources

https://github.com/lachlanharrisdev/go-std-markdown

• I have read CONTRIBUTING.md and the AI Usage Policy
• The project builds and runs successfully (i.e. go run .)
• Tests pass locally on my machine (i.e. go test ./...)
  • Relevant tests have been updated / created
  • Code passes linting checks (i.e. golangci-lint run; install)
• Relevant documentation has been updated / created (here)