Reorganize existing msg-related test suites under
a new `tests/msg/` subdir (matching `tests/devx/`
and `tests/ipc/` convention) and add unit tests for
the `_`-prefixed field filtering in `pformat()`.
Deats,
- `git mv` `test_ext_types_msgspec` and `test_pldrx_limiting` into
`tests/msg/`.
- add `__init__.py` + `conftest.py` for the new test sub-pkg.
- add new `test_pretty_struct.py` suite with 8 unit tests:
- parametrized field visibility (public shown, `_`-private hidden,
mixed)
- direct `iter_struct_ppfmt_lines()` assertion
- nested struct recursion filtering
- empty struct edge case
- real `MsgDec` via `mk_dec()` hiding `_dec`
- `repr()` integration via `Struct.__repr__()`
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi