Documentation overhaul

This meta-level issue tracks our refactoring of the Hypothesis documentation to follow diataxis, and to generally improve our documentation.

• add tutorial pages
  • phases
  • database
  • stateful (rewrite)
  • "adding notes" (rewrite)
  • deadline
  • filter rewriting. Maybe fits better under "explanation"; the user isn't doing anything.
• add explanation pages
  • "the lifetime of a hypothesis test" article + notes on the explain phase (scrutineer + inquisitor)
  • "Hypothesis database keys", how a database key is computed, what uniqueness level you can (generally) rely on
    • parametrization + test name + source code. Blank lines + decorators + comments are ignored
  • choice sequence and spans (draft exists in liam's docs branch)
    • link to this from the metadata.choice_nodes and metadata.spans observation docs, and throughout alternative backends
• add howto pages
  • "how to debug flaky tests"
  • "how to come up with properties"
  • "how to write efficient tests" (name tbd), about strategies overhead. Say that creating strategies per-test case (as with |st.data| and |st.composite|) can be slow. Particularly if the strategy can't be cached because its args are changing dynamically. Try rewriting to minimize the number of strategies you use, or increase cacheability.
  • https://github.com/HypothesisWorks/hypothesis/pull/4341#issuecomment-2780252954
• https://github.com/HypothesisWorks/hypothesis/pull/4315#discussion_r2009197810
• refactor "inferred types" in the API reference to distribute amongst st.builds, @given, register_type_strategy. And add a "working with types" tutorial or how-to
• reword settings.default https://github.com/HypothesisWorks/hypothesis/pull/4311#discussion_r2008627137
• consider numpy-style structured docstrings, especially for strategies (originally https://github.com/HypothesisWorks/hypothesis/issues/2957)
• document .patch file workflow with the pytest plugin https://github.com/HypothesisWorks/hypothesis/pull/3631
• https://github.com/HypothesisWorks/hypothesis/pull/4315#discussion_r2022111502
• https://github.com/HypothesisWorks/hypothesis/pull/4337#discussion_r2028053308
• https://github.com/HypothesisWorks/hypothesis/pull/4631#discussion_r3625268381
• https://github.com/HypothesisWorks/hypothesis/pull/4345#discussion_r2050001068
• figure out mechanics of redirects, possibly using https://github.com/documatt/sphinx-reredirects
  • systematically categorize which url targets to redirect
  • (^ done, but) might be worth redirecting popular url fragments on https://hypothesis.readthedocs.io/en/latest/details.html to the relevant
• improve (dynamically calculated) docstrings for settings
• stop shed from autoformatting code block examples to add newlines
• document .map and .flatmap as actual automethods on SearchStrategy, and link to them just like .filter
• merge testimonials into "projects that use hypothesis"? https://github.com/HypothesisWorks/hypothesis/pull/4340#discussion_r2029697693

Small stuff

• drop nose references, maybe test nose2 in CI? https://github.com/HypothesisWorks/hypothesis/pull/4341#discussion_r2030038791 place, like assume, target, random, type annotations, custom function execution, etc
• rework target() example? https://github.com/HypothesisWorks/hypothesis/pull/4311#discussion_r2000565650
• add docs test for xps namespace? https://github.com/HypothesisWorks/hypothesis/pull/4311#discussion_r2006919629
• cmd+f TODO_DOCS
• Verbosity vs settings.verbosity (+ same for Phase)