ENH: Use exactextract by default for zonalstats calculation

[KriWay-LV]

PR changes the default for zonalstats calculation to "exactextract".

Exactextract has a lot more options regarding which (parts of) pixels are counted in the zonal statistics and which aren't. Based on some tests:

• the negative buffer applied on the parcels was ???
• the stats being calculated were changed to ???

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.30%. Comparing base (a53c414) to head (abfc247).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #181      +/-   ##
==========================================
+ Coverage   70.84%   71.30%   +0.46%     
==========================================
  Files          37       38       +1     
  Lines        4863     4868       +5     
==========================================
+ Hits         3445     3471      +26     
+ Misses       1418     1397      -21     

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[theroggy]

Already some first small remarks while waiting on the performance/result tests being done...