build: finish the LTO and CI-parallelism change

[ResurrectedTrader]

706469f ("perf: Speed up CI + proper LTO") landed one file of that change, src/contract/game/GameLock.cpp, and nothing else. What is on main today is a tracked source file that no project compiles and that could not compile if one did, because the header still defines both thread-locals inline, plus a commit message describing link-time optimisation that is not actually enabled. This is the rest of it.

LTO

The ClangCL toolset ignores WholeProgramOptimization (no /GL equivalent reaches clang-cl), so Directory.Build.props turns the projects' Release setting into -flto. Objects become bitcode, llvm-lib archives them as-is, and lld-link runs the whole-program optimisation at link time. That is what lets the one-pointer game:: wrapper types inline across the static libs, which the architecture leans on.

That is also what GameLock.cpp was for. A COMDAT thread_local with a non-trivial destructor breaks lld's LTO (Associative COMDAT symbol ... does not exist), so GameReadLock::lock_ and GameWriteLock::manual_ are now declared in the header and defined in that file, and contract and js_tests compile it.

Parallelism

MultiProcessorCompilation lets each project compile its own sources across cores, MSBuild -m lets independent projects build at the same time, and EnforceProcessCountAcrossBuilds makes the two share one core-count budget instead of each spawning a full set of compilers.

CI

The release workflow ran tests in a second job that rebuilt the whole dependency tree just to run an executable the first job had already produced. Tests now run in build. The job that was serialised behind it becomes api, which reads only headers and so runs alongside build rather than after it.

Verification

Local, on this branch:

Check	Result
build.ps1 Release	succeeded, 0 warnings
build.ps1 test	127 passed
build.ps1 check-format	clean
build.ps1 lint	113 passed, 0 failed

lint is the one worth noting: it fails on main today, because it analyses GameLock.cpp and hits the redefinition described above. This is the change that makes it pass.