Add 100% test coverage for Rust code and CI workflow

- Add comprehensive unit tests for all traits:
  - Num trait: tested for all primitive integer types
  - SignNum trait: tested for all signed integer types
  - ToSigned trait: tested conversions for all integer types including edge cases
  - MaxValue trait: tested for all integer types
  - LinkType trait: tested for all unsigned integer types
- Add integration tests for combined trait usage
- Add edge case tests for unsigned-to-signed conversion wrapping behavior
- Add GitHub Actions workflow for Rust testing and coverage

Test coverage: 100% (67 tests)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: konard

.github/workflows/rust.yml

@@ -0,0 +1,60 @@
+name: Rust
+
+on:
+  push:
+    branches:
+      - 'main'
+    paths:
+      - 'rust/**'
+      - '.github/workflows/rust.yml'
+  pull_request:
+    branches:
+      - 'main'
+    paths:
+      - 'rust/**'
+      - '.github/workflows/rust.yml'
+
+defaults:
+  run:
+    working-directory: rust
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2022-08-22
+          components: rustfmt
+
+      - name: Run tests
+        run: cargo test --verbose
+
+      - name: Check formatting
+        run: cargo fmt -- --check
+
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2022-08-22
+          components: llvm-tools-preview
+
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+
+      - name: Generate code coverage
+        run: cargo llvm-cov --all-features --lcov --output-path lcov.info
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          files: rust/lcov.info
+          fail_ci_if_error: false