Add vcpkg integration

[jsrivaya]

Summary

Add vcpkg support so users in the vcpkg ecosystem (Windows/MSVC, game studios, Microsoft-adjacent teams) can consume loon without switching package managers.

Two-phase approach

Phase 1 — Overlay port in-repo (do this now)

Ship a vcpkg overlay port inside the loon repo. No registry PR process, no ongoing per-release maintenance burden, available immediately.

loon/
  vcpkg/
    ports/loon/
      portfile.cmake
      vcpkg.json

portfile.cmake (trivial for header-only):

vcpkg_from_github(
    OUT_SOURCE_PATH SOURCE_PATH
    REPO jsrivaya/loon
    REF "v${VERSION}"
    SHA512 <hash>
    HEAD_REF main
)

set(VCPKG_BUILD_TYPE release)
vcpkg_cmake_install()
vcpkg_cmake_config_fixup(CONFIG_PATH lib/cmake/loon)
file(REMOVE_RECURSE "${CURRENT_PACKAGES_DIR}/debug")
vcpkg_install_copyright(FILE_LIST "${SOURCE_PATH}/LICENSE")

vcpkg.json:

{
  "name": "loon",
  "version": "0.2.0",
  "description": "High-performance header-only C++ data structures",
  "homepage": "https://github.com/jsrivaya/loon",
  "license": "MIT",
  "dependencies": []
}

Users consume it with:

vcpkg install loon --overlay-ports=path/to/loon/vcpkg/ports

Document this in the README Installation section alongside the existing Conan instructions.

Phase 2 — Official vcpkg registry submission (defer until ~100-200 stars)

Submit a PR to microsoft/vcpkg to add loon to the public registry. This gives passive discoverability but requires:

• A PR to microsoft/vcpkg with portfile + versioning files
• Review process (can take days to weeks)
• A PR per release to update the version going forward

Not worth the maintenance overhead until there is meaningful adoption.

Acceptance criteria

• vcpkg/ports/loon/portfile.cmake added to repo
• vcpkg/ports/loon/vcpkg.json added to repo
• README Installation section updated with vcpkg overlay instructions
• CI verifies the overlay port installs cleanly (optional but recommended)