Audit remaining broad except ImportError guards (pandas, pydantic, trans auto-register) #7

Follow-up to #4 / #6. #6 narrowed the ju guard in specs.py so only the absence of ju itself falls back; any other import failure propagates. The same masking pattern remains elsewhere, guarding genuinely optional dependencies:

• uf/renderers.py (DataFrame renderer can_render): except ImportError: return False. A broken pandas install silently disables DataFrame rendering.
• uf/pydantic_support.py (is_pydantic_model, validation-error formatting): except ImportError. A broken pydantic install silently treats models as plain objects.
• uf/trans.py (module-level register_common_types()): except ImportError: pass around the whole registration. Any ImportError raised inside registration is swallowed at import time.

Suggested: one small shared helper, generalized from _import_func_to_form_spec in specs.py (return the module, or None only when ModuleNotFoundError.name is the optional package itself, otherwise re-raise), applied at these sites. Lower stakes than #4 because these really are optional deps, hence deferred.