Specification performance analysis tool

[jpn--]

The ability to write anything in a spec file is a footgun. See for example #904. We need a tool, suitable for the typical model developer, to measure the computational complexity (i.e. runtime) of individual expressions in spec files.

[jpn--]

Of note: the level of effort to make this happen in legacy mode (non-sharrow) is only a day or two of effort. Making it work for sharrow will be more complicated as the expression timing will either need to be embedded into the sharrow code generation or by manipulating the execution of sharrow code, either of which will be tricky.

[bhargavasana]

Can we close this since #936 is merged and sharrow profiler will be addressed when #937 is worked on?