Add PrecompileTools precompilation setup

[pbrehmer]

Here we add a precompilation setup using PrecompileTools.jl to cut down on the long time-to-first-execution (TTFX) of some functions (in particular anything involving AD takes a very long time to execute). The precompile.jl file covers most of the common uses but doesn't iterate through all possible permutations to still ensure that the initial precompilation doesn't take too long. Currently it takes a couple of minutes.

While this really speeds up the TTFX on the user side, it might be annoying from the developer side since any changes will result in re-precompilation of the package. This can be disabled by commenting out include("precompile.jl) locally or as described in the PrecompileTools docs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
src/PEPSKit.jl	87.50% <ø> (ø)
src/precompile.jl	100.00% <100.00%> (ø)

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[pbrehmer]

In principle this already works quite well I think. The only thing that is undesirable is that now all test individually have to run through the precompilation routine. Also I will try to speed things up further...

[pbrehmer]

Precompilation times now seem manageable:

• Ubuntu/Windows CI: ~10 mins
• MacOS CI: ~8 mins
• My local Ubuntu machine: ~7 mins

However, I had to take out all fermionic stuff from the workload since it more than doubles the precompilation times.

[pbrehmer]

While having a PrecompileTools setup does speed up TTFX quite a bit, it's not necessarily useful to have this precompiled by default and shipped with the package itself. I will add a page on PrecompileTools when we set up the new docs so that every user can set up their own precompilation routine. Let me close this PR for now :-)