[pax/fiddle refactor] Fixes for hoisting hparam calls.
[pax/fiddle refactor] Fixes for hoisting hparam calls.

* Include the class name in hoisted_function_name, to avoid name conflicts (e.g., in vanillanets.py)

* Add DoNotBuild tag to the dataclass field.

* In the hoisted autoconfig function: convert `SomeClass.HParams(...)` to `pax_fiddle.Config(SomeClass, ...)`, and *not* to `SomeClass(...)`.  In particular, this hoisted function needs to return a Fiddle config object from both the as_buildable path *and* the __call__ path.  In fact, the only reason we need to use auto_config here (rather than just setting configurable_factory=True on the field) is that we need it to be inlined in the _as_buildable path, so we can deeply configure it.

* Added a specialized version of `auto_config` at `pax_fiddle.auto_config` that adds `PaxConfig` to its auto-config exemption policy.

PiperOrigin-RevId: 482194070

google/praxis,google/praxis