Add contract WASM size budget checks

[newmattock]

Summary

• Add a CI workflow that enforces a 100 KB default WASM budget for each contract artifact.
• Add a reusable scripts/check-wasm-size.sh helper with WASM_SIZE_LIMIT_BYTES and SKIP_WASM_BUILD controls.
• Document local usage, CI behavior, and remediation steps for oversized contract builds.

Verification

• bash -n scripts/check-wasm-size.sh
• WASM_SIZE_LIMIT_BYTES=0 bash scripts/check-wasm-size.sh exits with the expected validation error.
• Attempted ./scripts/check-wasm-size.sh; local full build was blocked by environment issues after switching toolchains, then by disk exhaustion.

CI note

• The new WASM Size Budget / Contract WASM size check workflow passes on this PR.
• Existing CI / Test and Test Coverage jobs are red on workspace-wide formatting and test_proptest.rs HashSet<Address> issues that are outside this script/docs change.

Closes #496

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[greatest0fallt1me]

Merged via direct push to main (admin)