test(wasmtime): integration coverage for tvm-guest-rt typed accessors + reducers

Closes the test-coverage gap where tvm-guest-rt's wasm32-only
extern "C" declarations (and the byte arithmetic in `with_offset`)
had no end-to-end validation reachable from a host-target test run.

Approach: a WAT module that **faithfully reproduces** the call
sequences tvm-guest-rt emits — same tvm.* raw imports, same packed-
handle-with-delta arithmetic, same little-endian byte layout — and
exercises every reducer + typed-accessor path through it.

If host ABI for tvm.<op> ever drifts, this test catches it before
real guest code does.

#4 — Typed load/store integration (tvm-guest-rt::RegionPtr::load_*,
store_*):
  - typed_u8_round_trip — write/read every offset, verify pattern
  - typed_u32_le_round_trip — round-trip 0, 1, 0xdeadbeef, edges
  - typed_i64_le_round_trip — round-trip 0, ±MAX, ±MIN, mixed
  - typed_load_against_host_seeded_bytes — seed via write_bytes,
    read at non-zero deltas via the with_offset arithmetic; verifies
    both u8 (every offset) and u32_le (aligned offsets) paths

#5 — Reducer raw imports integration (tvm-guest-rt::RegionPtr::{sum_u8,
popcount, count_byte, count_in_range, min_max_u8, find_byte, eq,
lex_cmp, hash_fnv1a, and_fold_u8, or_fold_u8, xor_fold_u8,
sum_u32_le, max_u32_le, fill, xor_with_byte, xor_into_region}):
  - reducer_roundtrip_all_ops — exercises 14 reducer/comparison ops
    against a known byte pattern; checks scalar results match
    independently-computed references (sum, popcount, predicate
    counts, min_max, fold values for the 0..255 sequence, hash
    determinism, eq/lex_cmp on identical regions, sum/max u32_le).
  - reducer_mutators_modify_in_place — fill, xor_with_byte,
    xor_into_region; reads bytes back through TvmHost to confirm
    the in-place mutations took effect.

6 new tests, all passing. Total integration coverage now includes
every host-side reducer/mutator import that tvm-guest-rt exposes
plus the typed-accessor byte arithmetic.

Author: Zachary Whitley