[SizzleUnrlsd]

Summary

The two boxes left on #13, the PyIR instruction set of docs/architecture.md §6.

• Acceptance tests first (test: define PyIR import instructions and schema version), implementation follows.
• ir.model.Import: an effect instruction emitted for every alias of an import statement inside a function, with the module as written (relative dots included), the canonical symbol bound and the local name. Rule 3 of §39: the IR shows the import running where it stands. Uses of the name keep resolving to Symbol values, so no analysis changes; the instruction survives SSA and prints as import "json" as "j" @python.json. Module-level imports lower to nothing, ModuleIR holding functions only.
• PYIR_SCHEMA_VERSION, exported from coretrace_python.ir, versions the instruction set and joins the HIR, finding and plugin API versions in the persistent cache key.

Await and Yield of the same box landed in #36.

Closes #13