fixes https://git.clan.lol/clan/clan-core/issues/3791
This fixes multiple issues we had when re-generating shared vars.
Problem 1: shared vars are re-generated for each individual machine instead of just once (see #3791)
Problem 2: When a shared var was re-generated for one machine, dependent vars on other machines did not get re-generated, leading to broken state
Reviewed-on: https://git.clan.lol/clan/clan-core/pulls/5001
- Remove _serialized field from vars interface to prevent serialization
errors with throwing passBackend field
- Implement direct selection of generator fields using multi-select syntax
- Refactor vars_generators() to use new Generator.from_flake() method that
selects only safe fields (avoiding non-serializable values)
- Remove unused legacy methods: Generator.from_json(), Var.from_json(),
Prompt.from_json()
- Update precaching to match new selection approach
This fixes the serialization errors that were preventing vars from working
with the new password-store implementation by avoiding the problematic
_serialized field entirely.
