[io managers] remove special casing for Nothing outputs in io managers

[jamiedemaria]

Summary & Motivation

Our custom I/O managers have special cases written in that raise exceptions when an output is typed as Nothing. #18448 moves this logic of skipping the I/O manager so the main execution code path, so we can remove these special cases for the I/O managers. For DB I/O managers, we still need to raise an error when the return is None but doesn't have a Nothing typing type for consistency across versions.

How I Tested These Changes

[jamiedemaria]

Current dependencies on/for this PR:

• master
  • PR refactor _store_output so that outputs that do not invoke the I/O manager are immediately handled #18448
    • PR [for 1.6] Skip I/O manager when return type is Nothing  #17451
      • PR [io managers] remove special casing for Nothing outputs in io managers #18767 👈
        • PR [UPath I/O managers] skip store when return is None. Provide None at load if file doesnt exist #18975
          • PR [do not merge] Provide upstream asset materialization events to currently materializing asset #18916
            • PR [UPath I/O managers] special case handling of None outputs #18820
      • PR [prototype] skip I/O on return None #18718

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