Type-checker: i64 const literal requires explicit `as i64` cast (no context-typing / no integer suffix)

[star-ga]

Summary

An i64 const initialized with an integer literal is rejected: the literal infers as i32 and is not context-typed to the declared const type. The only accepted form is an explicit as i64 cast.

Repro

const X: i64 = 1;        // error[E2001]: const `X`: expected Scalar[i64] but found Scalar[i32]
const Y: i64 = 1i64;     // also error — integer suffix not supported
const Z: i64 = 1 as i64; // OK (the only accepted form)

Impact

Every i64 const with a literal value must be written <n> as i64, which is noisy at scale (e.g. a file with ~30 such consts needs the cast on every one).

Options

• (a) Context-type a const initializer literal to the declared const type (preferred — least surprise), or
• (b) support integer-literal suffixes (1i64, 255u8).

Add tests for both forms.