Forge JIT Backend Integration

[da-roth]

This PR integrates the Forge JIT backend for XAD, adding optional native code generation support. Forge is an optional dependency - everything builds and runs without it.

Changes

Build options added:

• QLRISKS_ENABLE_FORGE: Enable Forge JIT backend
• QLRISKS_ENABLE_FORGE_TESTS: Include Forge tests in test suite
• QLRISKS_ENABLE_JIT_TESTS: Enable XAD JIT tests (interpreter backend, no Forge)
• QLRISKS_BUILD_BENCHMARK / QLRISKS_BUILD_BENCHMARK_STANDALONE: Benchmark executables

Files added:

• test-suite/jit_xad.cpp: JIT infrastructure tests (interpreter backend)
• test-suite/forgebackend_xad.cpp: Forge backend tests
• test-suite/swaption_jit_pipeline_xad.cpp: JIT pipeline tests for LMM Monte Carlo
• test-suite/swaption_benchmark.cpp: Boost.Test benchmarks
• test-suite/benchmark_main.cpp: Standalone benchmark executable
• test-suite/PlatformInfo.hpp: Platform detection utilities
• .github/workflows/ql-benchmarks.yaml: Benchmark workflow

Files modified:

• CMakeLists.txt: Forge integration options
• test-suite/CMakeLists.txt: Conditional test/benchmark targets
• .github/workflows/ci.yaml: Added forge-linux and forge-windows jobs

Benchmarks

The benchmark workflow (ql-benchmarks.yaml) runs swaption pricing benchmarks comparing FD, XAD tape, JIT scalar, and JIT-AVX methods on Linux and Windows.

Also included some initial work towards #33 - the workflow has type overhead jobs that compare double vs xad::AReal pricing performance (no derivatives) on the same hardware, providing a baseline for measuring XAD type overhead.

Example benchmark run (Linux) Link

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