[evaleev]

Moves BTAS to the kit-cmake FindOrFetchBoost that builds Boost 1.92.0 when Boost is missing (ValeevGroup/kit-cmake#24). Part of the Boost upgrade across the ValeevGroup packages: SeQuant on Windows/MSVC needs Boost >= 1.85 (MSVC cannot compile Boost.Spirit 1.84). TiledArray, SeQuant, MPQC and TTG follow.

• kit-cmake pin → bbcf1ec (master, kit-cmake#24 merged).
• Boost floor 1.71 → 1.81, the same as the other ValeevGroup packages.
• CI: Ubuntu 22.04 → 24.04 (its Boost 1.83 meets the floor; 22.04 ships 1.74) with g++-14, as in TiledArray's CI.
• Install with Boost built from source: the kit now installs the Boost libraries BTAS uses and builds them with the default target, so the build-boost-in-BTAS target and the warning telling standalone users to build it before install are removed; README updated.

Verified on macOS (AppleClang):

• Boost fetched (system Boost hidden): check-btas 8/8; cmake --build + cmake --install installs BTAS and the Boost libraries; a downstream project find_package(BTAS) against the install tree builds and runs.
• Homebrew Boost 1.89: check-btas 8/8.

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