Fix vcpkg packaging: debug headers, DLL exports, YAML_USE_CXX17 typo, x86 exclusion

[Copilot]

vcpkg and CMake refinements

Decouple from snmalloc headers and add shared library (DLL) support

• Introduce include/trieste/compiler.h with self-contained TRIESTE_SLOW_PATH,
  TRIESTE_FAST_PATH, TRIESTE_LIKELY/UNLIKELY, and TRIESTE_USED_FUNCTION macros,
  replacing all uses of snmalloc/ds_core/defines.h macros throughout the
  headers (ast.h, intrusive_ptr.h, logging.h, pass.h, rewrite.h, wf.h).

• Make snmalloc an optional dependency controlled by TRIESTE_USE_SNMALLOC.
  When disabled, the core library no longer fetches or links snmalloc at all.
  The vcpkg port moves snmalloc from a hard dependency to an opt-in "snmalloc"
  feature.

• Add DLL export support for the JSON and YAML parser libraries:

  • Use CMake's GenerateExportHeader to produce json_export.h / yaml_export.h.
  • Annotate all public API functions with JSON_EXPORT / YAML_EXPORT.
  • Define JSON_STATIC_DEFINE / YAML_STATIC_DEFINE for static builds.
  • Rename output libraries to trieste-json / trieste-yaml.
  • Add a Windows shared-libs CI job (BUILD_SHARED_LIBS=ON).

• CMake modernisation:

  • Bump cmake_minimum_required to 3.28 and remove the cmake_utils
    dependency entirely. EXCLUDE_FROM_ALL is used natively on all
    FetchContent declarations.
  • Disable C++20 module scanning (CMAKE_CXX_SCAN_FOR_MODULES=OFF) since
    Trieste does not use modules.
  • Guard header installs on non-Debug builds to avoid installing into Debug
    prefixes.
  • Only define the clangformat target when snmalloc is available (it
    provides the clangformat_targets macro).

• vcpkg port fixes:

  • Prefix release tag refs with "v" to match actual Git tags.
  • Drop redundant PACKAGE_NAME from vcpkg_cmake_config_fixup.
  • Add "supports": "!x86" platform constraint.

• Fix C++17 compatibility in yaml reader (replace std::set::contains with
  find/end).

• Bump VERSION to 1.1.0.

[matajoh]

It would be good to test the DLL functionality on windows to ensure it is working properly.