[SizzleUnrlsd]

Closes #176. The engine side of the gRPC chantier; the grpc table follows in Enterprise (CoreTrace-Entreprise/coretrace-python-analyzer-plugins#3), with the pattern (?:^|\.)\w+_pb2_grpc\.\w+Servicer$ and the sources on ServicerContext.

Summary

• BasePattern(pattern, label, parameters=(None,), kinds=ALL). The methods of a class whose base's canonical symbol matches the regular expression are entry points, whatever the module's prefix and however the base is imported: module, module alias, import … as, name, name alias. The generated module may be in the project or absent from it.
• Parameters by their role. By position after self: None is attacker input of the model's kinds; a class symbol makes the parameter denote that class, so the sources on the class apply, as invocation_metadata() on a ServicerContext, without the object being input: peer() and str(context) give nothing. The message carries every kind, its MessageToDict conversion, attributes and dict literals included.
• RPC methods only. The arity must match the list. When the project holds the base (its class is a project symbol), only the methods the base defines are entry points, so a servicer's utility methods are not; otherwise every method with that arity is, which the tests document as the limit.
• Engine wiring. Signature and SignaturesAnalysis in the interprocedural layer, provided from the models at the four sites (single file, project, batch), like ClearingAnalysis. The call graph types the parameters by position for every resolvable base of the class: its inheritance map keeps the first base only, and a mixin or an installed class before the generated base would otherwise hide the context typing. SummaryIndex.defines says whether the project holds a class.
• Inheritance identifies a potential service; it does not prove the servicer is registered on a server (documented in the model and the guide).

Verification

• RED: 16 failures for the expected reasons (no finding, no entry point) once the model existed without behaviour; one more RED for the installed-first-base case, then fixed.
• tests/test_base_patterns.py: 24 passed. Full suite under Python 3.12.10, regression snapshots included: 1434 passed. ruff check and mypy pass.
• Mutations, all killed: the arity check, the base-defines check, the project-holds-base check, a typed role treated as input, patterns applied to decorators, the signature typing, the signature arity, the batch provisioning, the pattern's anchoring.