v0.32.0-rc1

[borg323]

In this release, the code has been reorganized and undergone major changes. Therefore this changelog will be less detailed and describe the changes in major groups.

• We have a new search API that allows search algorithms to co-exist. Currently available are classic (the default), dag-preview (more later), valuehead and policyhead. The default algorithm can be changed either at build time by the default_search option or by renaming the executable to include the algorithm name (e.g. lc0-valuehead).
• We also have a new backend interface that is chess oriented and not tied to the network architecture. The existing backends still use the old interface through a wrapper.
• The source code is reorganized, with a more logical directory structure.
• The original search was ported to the new search and backend interfaces and is renamed to classic. This has allowed some streamlining and simplifications.
• The dag-preview search is the DAG algorithm that lived in a separate branch up to now. It hasn't been so well tested, that's why it has "preview" in its name for now, but lives in the src/search/dag-classic directory.
• The valuehead search replaces ValueOnly mode and selects the move with the best value head evaluation.
• The policyhead search is equivalent to a single node search, selecting the best move using just the policy head.
• The new default_backend build option allows to override the fixed priority for the backend used by default.
• The new native_arch build option to override the -march=native compiler default for linux release builds, to help with distribution package creation.
• We have a new sycl backend that will work with amd, intel and nvidia gpus.
• There is also a new onnx-trt backend, using tensorrt on nvidia gpus.
• Support simple/normal/pro mode in options was cleaned up, using a common mechanism.
• Added the wait uci extension command to allow running simple tests from the command line.
• Removed the fen uci extension command as it was unnecessarily complicating things.
• Some preliminary fp8 support was added for onnx and xla. This is not functional, just there to make experimentation easier.
• Several build system changes and improvements.
• We now generate binaries for cuda 12, onnx-trt and macos.
• Support for using lc0 with openbench.
• New bench mode for a quicker benchmark.
• Assorted small fixes and improvements.

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This discussion was created from the release v0.32.0-rc1.