ci: confirm build works for all targets both locally and in CI process

[andrewb1269]

Confirm all build types work for all targets both locally and in the CI pipeline.

[jjohannes]

PR to solve this is ready: #263

• Gets the CI setup to building (including C++ crates and MacOS SDKs)
• Documents what needs to be done to get that all working locally on a Mac
  • Issue created to possibly automate more: Rust: automatically install LLVM for 'clang-cl' and 'llvm-lib' used in Windows cross-compilation hiero-gradle-conventions#97

[anthony-swirldslabs]

To clarify the problem statement, or rather the desired outcome: we want a Gradle build by default to build binaries for the host platform only. E.g. if I build on a modern Mac, the build should only build for Darwin aarch64 by default.

A special target and/or an option should be added to Gradle to force cross-compilation for all platforms at once (or select platforms - knowing that we have to build some binaries separately, e.g. the Mac binaries.) This would only be used in CI/GitHub. Developers almost never need this kind of a build locally, at least not by default.

[jjohannes]

Issue to solve this in the Gradle plugins: hiero-ledger/hiero-gradle-conventions#326