Catch more edge cases, add corresponding tests

[teutoburg]

Also support creation from list of tuples, as the normal dict does.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (c7ffaa8) 98.14% compared to head (f6c5a5b) 99.71%.

❗ Current head f6c5a5b differs from pull request most recent head 022652e. Consider uploading reports for the commit 022652e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #5      +/-   ##
==========================================
+ Coverage   98.14%   99.71%   +1.57%     
==========================================
  Files           5        5              
  Lines         323      355      +32     
==========================================
+ Hits          317      354      +37     
+ Misses          6        1       -5     

Files	Coverage Δ
tests/test_nested_mapping.py	100.00% <100.00%> (ø)
astar_utils/nested_mapping.py	99.17% <94.11%> (+4.72%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.