ci: add WASM no-std compliance check to pipeline

[Mirabel64]

Summary

Resolves #12 by adding a dedicated cargo check --target wasm32-unknown-unknown --lib step to the client-checks job in .github/workflows/ci.yml.

Problem

README.md documents the cargo check --target wasm32-unknown-unknown --lib no-std compliance check, but it was not exercised in CI. A stray use std::... or println! would compile fine under cargo test on the host (which re-enables std via the test harness) yet fail at deployment time.

Fix

Add a single step right after the existing toolchain install (which already pulls the wasm32-unknown-unknown target):

- name: WASM no-std compliance check
  working-directory: apexchainx_calculator
  run: |
    cargo check --target wasm32-unknown-unknown --lib 2>&1 | tee no_std_check.log \
      || (echo "=== no_std compliance check failed: std imports are not allowed in WASM ===" \
          && cat no_std_check.log && exit 1)

Pattern mirrors the existing Cargo check step (host) so logs are consistent on failure.

Acceptance criteria from #12

• CI includes a wasm32 no-std check.
• Runs on every push/PR (job covers on: push and pull_request).
• Installs wasm32 target (already installed by the prior toolchain step in the client-checks job).
• Fails if a std import is introduced.
• Passes on the current codebase — lib.rs declares #![no_std] and a project-wide grep finds no use std:: references.

Closes #12

[Icahbod]

LGTM