[SizzleUnrlsd]

Closes #95.

What

The taint engine consulted Sanitizer models only in the ExternalSymbol branch without an interprocedural summary. A Sanitizer declared on a function of the analysed project was therefore inert: a code base could not declare its own validation layer.

• declared_clean(symbol, result): after known() computes the result of a project-function call, a Sanitizer declared on that function strips its kinds from the result. The flows and side effects the summary reports inside the callee are kept — only the returned taint changes.
• Applied on both branches: ExternalSymbol with a project summary (other file) and KnownFunction (same file). The same-file symbol is project_symbol(module, name), so _TaintProblem/propagate_taint gain a module parameter that TaintAnalysis.compute fills from ctx.module.name.

Tests

• test_a_sanitizer_declared_on_a_project_function_overrides_its_summary — same file; asserts the flow exists without the model.
• test_a_sanitizer_declared_on_a_function_of_another_file_refutes_the_flow — cross-file, through a real plugin directory loaded next to the bundled ones; asserts the finding exists without it.

Full suite: 891 passed. ruff check and mypy src clean.

Docs

Usage guide gains "Your own validation layer" showing Sanitizer and Validator on project symbols (the Validator case was verified to refute a guarded flow); changelog entry under Unreleased.