ci: add ROCm 7.14 support and support more architectures, drop ROCm 6.2 and 6.3

[sstamenk]

Summary

• Add ROCm 7.14.0 to the Linux and Windows CI build matrix.
• Use the official rocm/dev-ubuntu-22.04:7.14.0-full image for Linux builds.
• Install the Windows 7.14 development toolchain from AMD's TheRock multi-architecture package index.
• Preserve the legacy repo.radeon.com installation path for Windows ROCm 7.2.1.
• Add ROCm 7.14 architecture coverage:
  • Linux: gfx908 and gfx1030-gfx1036
  • Windows: gfx1030-gfx1036 and gfx1152, gfx1153
• Introduce reusable version-threshold checks so future ROCm releases inherit architecture and packaging changes correctly.
• Drop ROCm 6.2 and 6.3 builds, making ROCm 6.4 the minimum supported version.
• Update the installation guide with the new supported versions, targets, and Windows source-build instructions.

[github-actions]

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[matthewdouglas]

LGTM, thanks!