Vector class updates

[paleolimbot]

This PR eliminates the s2_lnglat and s2_point vector classes to use wk's xy() and xyz() with special CRS values. The wk classes are much, much, faster!

Fixes #159.

[codecov-commenter]

Codecov Report

Merging #181 (50180e8) into main (6134c0e) will decrease coverage by 0.04%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##             main     #181      +/-   ##
==========================================
- Coverage   93.67%   93.62%   -0.05%     
==========================================
  Files          50       49       -1     
  Lines        3541     3483      -58     
==========================================
- Hits         3317     3261      -56     
+ Misses        224      222       -2     

Impacted Files	Coverage Δ
R/vctrs.R	100.00% <ø> (+20.00%)	⬆️
R/s2-lnglat.R	83.33% <81.81%> (-16.67%)	⬇️
R/s2-point.R	92.30% <92.30%> (-7.70%)	⬇️
R/s2-cell.R	100.00% <100.00%> (ø)
R/s2-geography.R	98.30% <100.00%> (ø)
src/s2-lnglat.cpp	100.00% <100.00%> (+3.44%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6134c0e...50180e8. Read the comment docs.