🔀🔧 MERGE: Add strict typing for most sphinx_needs modules

[chrisjsewell]

This PR adds strict typing to most of the package, building on #987 and #998 to try to confine use of dynamic types to a small surface area.
This hopefully makes it easier for developers to navigate the code base, and lessens the potential for bugs arising from type mismatches.

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There are still some open questions, particularly around NeedsInfoType, which

1. has some dynamic fields (such as user defined links/options) and,
2. has some fields which are only set after post-transforms (such process_need_nodes)

[chrisjsewell]

Will be fixed by #1003