[tuner] Add unified compilation step for models and dispatches

[Max191]

This PR adds a new compile() function for compiling both models and dispatches during tuning. This will eventually replace the old path, which has a separate function for model compilation and dispatch compilation. The new compilation flow is now simpler:

1. Populate each CandidateTracker with the input and output filepaths. The input filepaths can be overridden by an optional function argument to the compile() function. This argument can be used for model tuning, passing the model filepath as the new input file.
2. For each candidate, strip the compilation info using iree-opt, and compile to a vmfb with the iree compiler python bindings. Set the candidate's TD spec file (generated during candidate generation), and add any additional iree-compile flags that came from the TuningClient. The extra flags are taken from a new abstract TuningClient function called get_iree_compile_flags.
3. For all successful compilations, save the vmfbs to the designated output path, and skip any failed compilation. For any failed compilation, a failure dump is saved instead of the vmfb.
4. Remove duplicate vmfbs, and return the ids of all unique candidates.

[Max191]

This PR is based on #606. Please only review the last commit.