Implement multi-platform build system with pure Go support

- Introduced a comprehensive build system that supports multiple platforms (Linux, macOS, Windows, Android) using pure Go builds (`CGO_ENABLED=0`).
- Updated all build and test scripts to ensure compatibility with the new purego approach, allowing for dynamic loading of `libsecp256k1` at runtime.
- Added detailed documentation on the build process, platform detection, and deployment options.
- Enhanced CI/CD workflows to automate builds for all supported platforms and include necessary libraries in releases.
- Updated `.gitignore` to exclude build output files.
- Created new documentation files for deployment and multi-platform build summaries.

LIBSECP256K1_DEPLOYMENT.md

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+# libsecp256k1 Deployment Guide
+
+All build scripts have been updated to ensure libsecp256k1.so is placed next to the executable.
+
+## Updated Scripts
+
+### 1. GitHub Actions (`.github/workflows/go.yml`)
+- **Build job**: Installs libsecp256k1 from source, enables CGO
+- **Release job**: Builds with CGO, copies `libsecp256k1.so` to release-binaries/
+- Both the binary and library are included in releases
+
+### 2. Deployment Script (`scripts/deploy.sh`)
+- Builds with `CGO_ENABLED=1`
+- Copies `pkg/crypto/p8k/libsecp256k1.so` next to the binary
+- Installs both binary and library to `$GOBIN/`
+
+### 3. Benchmark Script (`scripts/benchmark.sh`)
+- Builds benchmark binary with `CGO_ENABLED=1`
+- Copies library to `cmd/benchmark/` directory
+
+### 4. Profile Script (`cmd/benchmark/profile.sh`)
+- Builds relay with `CGO_ENABLED=1`
+- Copies library next to relay binary
+- Copies library to benchmark run directory
+
+### 5. Test Deploy Script (`scripts/test-deploy-local.sh`)
+- Tests build with `CGO_ENABLED=1`
+- Verifies library is copied correctly
+
+## Runtime Requirements
+
+The library will be found automatically if:
+1. It's in the same directory as the executable
+2. It's in a standard library path (/usr/local/lib, /usr/lib)
+3. `LD_LIBRARY_PATH` includes the directory containing it
+
+## Distribution
+
+When distributing binaries, include both:
+- `orly` (or other binary name)
+- `libsecp256k1.so`
+
+Users can run with:
+```bash
+./orly
+```
+
+Or explicitly set the library path:
+```bash
+LD_LIBRARY_PATH=. ./orly
+```
+
+## Building from Source
+
+All scripts automatically handle the library placement:
+```bash
+# Deploy to production
+./scripts/deploy.sh
+
+# Build for local testing
+CGO_ENABLED=1 go build -o orly .
+cp pkg/crypto/p8k/libsecp256k1.so .
+```
+
+## Test Scripts Updated
+
+All test scripts now ensure libsecp256k1.so is available:
+
+### Test Scripts
+- `scripts/runtests.sh` - Sets CGO_ENABLED=1 and LD_LIBRARY_PATH
+- `scripts/test.sh` - Sets CGO_ENABLED=1 and LD_LIBRARY_PATH
+- `scripts/test_policy.sh` - Sets CGO_ENABLED=1 and LD_LIBRARY_PATH
+- `scripts/test-managed-acl.sh` - Sets CGO_ENABLED=1 and LD_LIBRARY_PATH
+- `scripts/test-workflow-local.sh` - Matches GitHub Actions with CGO enabled
+
+### Docker Files
+- `cmd/benchmark/Dockerfile.next-orly` - Copies libsecp256k1.so to /app/
+- `cmd/benchmark/Dockerfile.benchmark` - Builds and includes libsecp256k1
+
+All test environments now have access to libsecp256k1.so for CGO-based cryptographic operations.