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

❌ Patch coverage is 60.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.65%. Comparing base (867974e) to head (cc950a1).

Files with missing lines	Patch %	Lines
...zonal_stats_bulk/_zonal_stats_bulk_exactextract.py	40.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #181      +/-   ##
==========================================
+ Coverage   34.60%   35.65%   +1.05%     
==========================================
  Files          37       38       +1     
  Lines        4890     4894       +4     
==========================================
+ Hits         1692     1745      +53     
+ Misses       3198     3149      -49     

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[theroggy]

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