Simplified trait bounds.

[ryzhyk]

Simplified trait bounds in distinct.rs and window.rs (missed them during recent refactoring).

@gz, with this you shouldn't need encode/decode bounds in these files in #124.

[codecov]

Codecov Report

Merging #213 (d72bbd9) into main (2cb2a8b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #213   +/-   ##
=======================================
  Coverage   84.06%   84.07%           
=======================================
  Files         127      127           
  Lines       23460    23452    -8     
=======================================
- Hits        19722    19717    -5     
+ Misses       3738     3735    -3     

Impacted Files	Coverage Δ
src/operator/time_series/window.rs	98.63% <ø> (ø)
src/operator/distinct.rs	94.55% <100.00%> (-0.09%)	⬇️
src/nexmark/generator/bids.rs	98.40% <0.00%> (-0.80%)	⬇️
src/time/nested_ts32.rs	72.60% <0.00%> (ø)
src/trace/spine_fueled.rs	83.61% <0.00%> (+0.37%)	⬆️
src/circuit/dbsp_handle.rs	92.57% <0.00%> (+0.99%)	⬆️

[gz]

lgtm will update my branch after this is merged