waveshare213v2: Make busy a PinIn, use WaitForEdge

[hansmi]

The busy pin from the e-paper display is only used to read, not to
write, and thus there's no need for the PinIO interface. PinIn is
enough.

In addition the WaitForEdge function can be used to shorten the delays
when waiting for the display to become idle. Spurious or missed edges
are acceptable: the delay isn't very long.

[codecov-commenter]

Codecov Report

Merging #40 (45561a7) into main (5179e40) will increase coverage by 0.0%.
The diff coverage is 0.0%.

@@          Coverage Diff          @@
##            main     #40   +/-   ##
=====================================
  Coverage   62.5%   62.5%           
=====================================
  Files         55      55           
  Lines       6720    6723    +3     
=====================================
+ Hits        4202    4204    +2     
- Misses      2377    2378    +1     
  Partials     141     141           

Impacted Files	Coverage Δ
waveshare2in13v2/errorhandler.go	0.0% <0.0%> (ø)
waveshare2in13v2/waveshare213v2.go	0.0% <0.0%> (ø)
as7262/as7262.go	99.3% <0.0%> (+0.7%)	⬆️

---

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 5179e40...45561a7. Read the comment docs.