Fix URL validation + housekeeping

[FynnBe]

set out to investigate #663 possibly caused by pydantic/pydantic#10925
but ended up avoid the issue by pinning pydantic in #671.

Let's wait for the next pydantic release to see if this needs further 'fixing' or if we just avoid some pydantic 2.10 releases...

So this PR just cleans up some code and fixes an issue with URL validation I encountered when adding more tests.

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
4877	3769	77%	70%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
bioimageio/spec/_internal/common_nodes.py	90%	🟢
bioimageio/spec/_internal/type_guards.py	84%	🟢
bioimageio/spec/_internal/url.py	95%	🟢
bioimageio/spec/_internal/validated_string.py	100%	🟢
bioimageio/spec/_internal/validation_context.py	96%	🟢
bioimageio/spec/_io.py	63%	🟢
bioimageio/spec/application/v0_3.py	100%	🟢
bioimageio/spec/common.py	100%	🟢
bioimageio/spec/dataset/v0_3.py	96%	🟢
bioimageio/spec/generic/v0_3.py	91%	🟢
bioimageio/spec/model/v0_5.py	68%	🟢
bioimageio/spec/notebook/v0_3.py	100%	🟢
TOTAL	90%	🟢

updated for commit: 44aa991 by action🐍