fix nan to num inverse

[arrjon]

Fix the nan_to_num inverse in the adapter: there was a minor bug when a key was missing in the inverse function

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
bayesflow/adapters/transforms/nan_to_num.py	0.00%	2 Missing ⚠️

Files with missing lines	Coverage Δ
bayesflow/adapters/transforms/nan_to_num.py	68.42% <0.00%> (-3.81%)	⬇️

... and 10 files with indirect coverage changes