Add sqrt; fix domains in function testsuite; update freeze of sp.Pow

Closes #123 (closed)

• Add the sqrt function to the IR, as well as to CPU, CUDA, SYCL, and x86-vector targets
• Rewrite case for sp.Power in freeze to generate sqrt calls where appropriate
• Adapt function test suite: Test on values within the correct domain for all functions
• Untrack some testsuite output files
• Remove some deprecated imports from the testsuite