Release v0.2.0

Release: v0.2.0 [skip ci]

Minor

• Add: Metal draft (db0dc92)

Patch

• Docs: File headers (e1ac216)
• Make: Switch to .cuh extension for CUDA (37c0581)
• Make: Drop deprecated assets (f311a61)
• Fix: Missing fmt include for OpenCL (0c0bc0f)
• Fix: Feature-testing __cpp_lib_execution (0c80b36)
• Make: Switch to .cuh extension for CUDA (818851f)