Re-enable Float16 tests.

[maleadt]

I've fixed the PoCL (next) build and backported pocl/pocl#2224 so that fp16 now works fully:

julia> using pocl_next_jll, OpenCL

julia> OpenCL.versioninfo()

Available platforms: 3
 - Portable Computing Language
   OpenCL 3.0, PoCL 7.2  Linux, Release, RELOC, SPIR-V, LLVM 20.1.2jl, SLEEF, DISTRO, POCL_DEBUG
   · cpu-skylake-avx512-AMD Ryzen 9 9950X 16-Core Processor (svm:c+f, usm:h+d, bda, fp16, fp64, il)

vs. before we didn't advertise it:

julia> using pocl_jll, OpenCL

julia> OpenCL.versioninfo()

Available platforms: 3
 - Portable Computing Language
   OpenCL 3.0, PoCL 7.1  Linux, Release, RELOC, SPIR-V, LLVM 20.1.2jl, SLEEF, DISTRO, POCL_DEBUG
   · cpu-skylake-avx512-AMD Ryzen 9 9950X 16-Core Processor (svm:c+f, usm:h+d, bda, fp64, il)

Closes #312.
Only to be merged after pocl/pocl#2224 or the pocl:local CI job will fail.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.62%. Comparing base (9a142d8) to head (fd363ae).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #452      +/-   ##
==========================================
- Coverage   82.96%   80.62%   -2.34%     
==========================================
  Files          13       13              
  Lines         898      898              
==========================================
- Hits          745      724      -21     
- Misses        153      174      +21     

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