Complete FFI bindings and CI integration for native crypto

FFI Bindings Implementation:
- Complete Dart FFI bindings for Rust crypto library
- Add ffi package dependency
- Implement proper memory management with malloc/calloc
- Full FFI function signatures for all crypto operations:
  * fuego_generate_keys
  * fuego_private_to_public
  * fuego_generate_address
  * fuego_validate_address
  * fuego_key_to_mnemonic
  * fuego_mnemonic_to_key
  * fuego_validate_mnemonic
- Safe pointer handling with proper cleanup

CI Workflow Updates:
- Add Rust toolchain setup for all platforms
- Build Rust library for:
  * macOS (x86_64 and arm64)
  * Windows (x86_64)
  * Linux (x86_64)
- Add Rust cache for faster builds
- Copy built libraries to assets/bin/
- Platform-specific library names

Architecture:
- Native crypto operations via FFI when available
- Automatic fallback to RPC when native unavailable
- Memory-safe pointer management
- Zero-copy operations where possible

Ready for testing and UI integration

Author: ColinRitman

.github/workflows/xfg-wallet-desktop.yml

@@ -122,6 +122,22 @@ jobs:
           flutter-version: '3.24.0'
           channel: 'stable'
 
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Set up Rust cache
+        uses: swatinem/rust-cache@v2
+
+      - name: Build Rust crypto library
+        run: |
+          cd native/crypto
+          cargo build --release --target x86_64-pc-windows-msvc
+
+      - name: Copy Rust library to assets
+        run: |
+          New-Item -ItemType Directory -Force -Path assets\bin
+          Copy-Item native\crypto\target\x86_64-pc-windows-msvc\release\fuego_crypto.dll assets\bin\fuego_crypto.dll
+
       - name: Enable Windows desktop support
         run: flutter config --enable-windows-desktop
 
@@ -185,6 +201,22 @@ jobs:
           flutter-version: '3.24.0'
           channel: 'stable'
 
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Set up Rust cache
+        uses: swatinem/rust-cache@v2
+
+      - name: Build Rust crypto library
+        run: |
+          cd native/crypto
+          cargo build --release --target x86_64-unknown-linux-gnu
+
+      - name: Copy Rust library to assets
+        run: |
+          mkdir -p assets/bin
+          cp native/crypto/target/x86_64-unknown-linux-gnu/release/libfuego_crypto.so assets/bin/libfuego_crypto.so
+
       - name: Download xfg-stark-cli
         run: |
           curl -L -o xfg-stark-cli-linux.tar.gz "https://github.com/ColinRitman/xfgwin/releases/download/v0.8.8/xfg-stark-cli-linux.tar.gz"