Restoring typeguard functionality

[jamesbraza]

To get typeguard to work you need to not import the target package into conftest.py. We were doing that, so to not do that:

• Using lmi imports where possible
• Lazily importing the rest

Then, I resolved all type errors that were exposed.

[Copilot]

Pull Request Overview

This PR restores typeguard functionality by refactoring the import structure to delay importing certain packages and updating type annotations to support multiple value types.

• Introduce lazy imports in tests/conftest.py and agent test fixtures to avoid typeguard errors.
• Update type annotations for missing replacement parameters across multiple functions using Mapping.
• Refactor header usage in client modules to use lmi.utils constants.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/conftest.py	Lazily import paperqa modules to avoid typeguard instrumentation.
paperqa/utils.py	Updated missing_replacements type to Mapping for added flexibility.
paperqa/types.py	Annotated CITATION_FALLBACK_DATA with an explicit mapping type.
paperqa/clients/semantic_scholar.py	Updated header usage to use the constant from lmi.utils.
paperqa/clients/crossref.py	Updated missing_replacements types and refactored fragments loop.

Comments suppressed due to low confidence (1)

tests/conftest.py:112

• There is a duplicated word 'is' in the question string; please change it to 'What is a self-explanatory model?'.

return PQASession(question="What is is a self-explanatory model?")