Transform writer's guide

[t-vi]

Having written a few "new-style" transforms between a few people, we might compile a guide:

• intervention points for transforms in the thunder.jit flow,
• expected trace properties and how they might break and how to preserve them (and checking them in debug mode #1180 ),
• tooling
  • lower level / editing traces directly
    • handling proxies (new, replace, ...)
    • finding things (produces and consumers)
    • scopes
    • sym.bind(...) vs. sym(...) vs. bsym.from_bsym and when to use what,
    • bsym.from_bsym_swap_proxies
    • adding inputs and outputs,
  • higher level
    • interpret_trace,
    • visitor_transform,

(feel free to add)

cc @borda @apaz-cli @riccardofelluga

[t-vi]

use of scopes (see also https://github.com/Lightning-AI/lightning-thunder/issues/935 )