gen-zig types a local by its name across the whole use closure, so two specs with the same local name and different types cannot be imported together #11216

Part of the compiler defects of #5980, found by the M5c lane (PR #11215) of the night loop #11063. t27c test-report (the Zig backend) types a local variable by its NAME across the whole use closure: in specs/analog/sar_kick.t27 a local half : f64 made (half as u64) in specs/analog/mos_table.t27's blend1_w, where half is a u32, a float-to-int conversion, so no spec could import both files. The result was a compile error in t27c test-report; t27b test did not see it. The lane renamed the field and the local to hw in sar_kick.t27 to land its work; the compiler is unchanged.

Goal

Two functions in different modules of one closure that each declare a local of the same name with different types compile independently, in the Zig backend as in t27b.

Requirements

• FR-001: The Zig backend MUST scope the type of a local to its own function; a local named half in one module MUST NOT change the type of a half in another module's function.
• FR-002: A minimal repro MUST be committed as a conformance vector: two modules, one with var half : f64 and a function using it, one with const half : u32 cast to u64 in another function, both imported by a third spec whose test calls both.
• FR-003: The fix MUST follow the FROZEN_HASH ceremony or live in .t27 where the emitter is ported; no hand-written Rust may grow.

Scenarios

• Given the repro of FR-002, when t27c test-report runs, then it compiles and the test passes, and t27b test gives the same verdict.
• Given the repo at the commit before the rename in sar_kick.t27, when t27c test-report runs on a spec that imports sar_kick.t27 and mos_table.t27, then it compiles.

Boundary

• bootstrap/src/compiler.rs
• specs/tri/t27b/conformance/same_local_name.t27

Success Criteria

• t27c test-report specs/tri/t27b/conformance/same_local_name.t27 exits 0 with 0 vacuous passes.
• t27c parse-conform exits 0 with the same vector counts as before plus the new vector.