Add naming-semantics tests for URDF assembly; fix name_case propagation bug

[Copilot]

component_prefix patching and name_case policy changes in the URDF assembly manager had no test coverage, and a bug caused name_case updates to never actually reach URDFComponentManager._name_case.

Bug fix — URDFComponentManager missing name_case property setter

URDFAssemblyManager.name_case setter called self.component_manager.name_case = ..., but URDFComponentManager had no property setter, so Python silently created a dangling instance attribute while _name_case remained unchanged. Added a proper getter/setter to URDFComponentManager:

# Before: setting name_case on the assembly manager had no effect on
# URDFComponentManager._name_case — links/joints were still cased with
# the original defaults regardless of the policy set.

manager = URDFAssemblyManager()
manager.name_case = {"joint": "lower", "link": "upper"}
assert manager.component_manager._name_case == {"joint": "lower", "link": "upper"}
# ^^^ AssertionError before fix

The new setter mirrors the constructor's lenient-validation strategy (warn + ignore invalid entries) and documents the intentional divergence from URDFAssemblyManager.name_case which raises ValueError.

New tests — tests/toolkits/test_urdf_assembly_naming.py

21 tests using minimal inline URDF fixtures across four focused test classes:

Class	What it covers
TestUnknownComponentKeyRaises	Unknown/non-string component keys and non-list inputs raise ValueError
TestComponentPrefixPreservesOrder	Patch-style prefix updates don't reorder; cumulative patches work; unpatched components keep original prefixes
TestNameCaseAffectsNames	upper/lower/none modes applied to link and joint names; setter validation; policy propagation to URDFComponentManager
TestSignatureChangesWithNamingSettings	Changing component_prefix or name_case produces a distinct assembly signature (cache invalidation)

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