Provide fusepy with the file system encoding

[vxgmichel]

Also use EINVAL as fallback error code in fuse operations.

[codecov]

Codecov Report

Merging #827 into master will increase coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #827      +/-   ##
==========================================
+ Coverage   80.09%   80.12%   +0.02%     
==========================================
  Files         263      263              
  Lines       21660    21662       +2     
==========================================
+ Hits        17349    17357       +8     
+ Misses       4311     4305       -6

Impacted Files	Coverage Δ
parsec/core/mountpoint/fuse_operations.py	39.47% <0%> (ø)	⬆️
parsec/core/mountpoint/fuse_runner.py	97.16% <100%> (+0.05%)	⬆️
parsec/core/gui/users_widget.py	81.54% <0%> (-2.98%)	⬇️
parsec/core/fs/remote_loader.py	76.2% <0%> (+0.4%)	⬆️
parsec/core/fs/workspacefs/entry_transactions.py	96.57% <0%> (+0.57%)	⬆️
parsec/core/fs/workspacefs/workspacefs.py	96.72% <0%> (+0.65%)	⬆️
parsec/core/sync_monitor.py	94.87% <0%> (+0.85%)	⬆️
parsec/backend/postgresql/block.py	90.14% <0%> (+1.4%)	⬆️
parsec/core/backend_connection/transport.py	92.48% <0%> (+1.5%)	⬆️
parsec/api/transport.py	90.98% <0%> (+1.63%)	⬆️

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