fix: cargo fmt on hash module

[kacy]

summary

• run cargo fmt on two files that were out of format after the packed hash encoding PR (perf: packed hash encoding to reduce memory ~451 → ~240 B/key #276):
  • crates/ember-core/src/keyspace/hash.rs — long iterator chain line wrap
  • crates/ember-core/src/types/hash.rs — function signature line wrap

this was the only CI failure (the check job's cargo fmt --all --check step).

what was tested

• cargo fmt --all --check passes
• cargo clippy --all-targets --all-features -- -D warnings passes
• all 123 integration tests pass (--test-threads=1)