Logarithm axes in plots library

[jamesrswift]

This is a very early draft, but as this has been a highly sought after feature, I'm making this draft PR public to allow for collaboration.

This implementation adds axis options {x}-mode that takes "lin" (default) or "log", which is passed through context to _prepare for scaling in plot-space (the infinite xy plane) to take place, which passes it forward to util.compute-stroke-paths and util.compute-fill-paths. Concurrently, ticks are then calculated from compute-logarithmic-ticks which applies the inverse of that transformation on tick marks.

Implementation quirks:

• axis parameters such as min and max are not transformed in any way. This flaw can be fixed with a good deal of work, so it may not be worth the effort,

To do:

• Provide a better heuristic for choosing tick mark locations in compute-logarithmic-ticks. Its a copy/paste of the linear one at the moment because I wanted to see it working
• The rendering of the grid will need changing as well
• Support bases other than base 10
• Move scaling from prepare to a more suitable location

I'm sure there's more but its late. This is very much open for feedback even in its draft state because its definitively a feature to get right on the first attempt.

Pretty pictures:

[jamesrswift]

Current state:

[jamesrswift]

Minor tick marks seem to be a tricky thing here - not sure what a good heuristic is. I think minor tick steps should be exponents? Like should a tick step of 0.5 would place a tick half way between powers?

[jamesrswift]

Since the recent commit allowing custom function transforms I made a new branch from that commit as I wanted to change the tactic I was going with. I'll close this PR as the branch isn't going to be updated, and I'll make a new PR from the new branch once I get a barely working implementation ... working. For anyone interested in following before then, I'm doing the work here: https://github.com/JamesxX/cetz-plot/tree/log-mode-attempt-3 (yes there was an attempt 2 that went in the box of deleted shame)