[CI] Add wasm binary size regression check to ci.yml

[davidmaronio]

Context

ci.yml builds the release wasm target but does not track or fail on binary size growth. A simple size-diff check against a baseline would catch unexpected bloat from new dependencies or unused code before merge.

Acceptance criteria

• Behavior/gap described above is addressed or confirmed and documented
• Relevant unit test(s) added or updated
• cargo fmt --check and cargo clippy --all-targets --features testutils -- -D warnings pass

Files to touch

.github/workflows/ci.yml

Out of scope

• Unrelated refactors outside the files listed above
• Changes to unrelated contract functions not mentioned in this issue