Add ability to update package definitions + auto-propagate to dependents

[OceanOak]

In this PR:

• fn, type, and val commands now detect updates to existing definitions, creates a new version with a new UUID and repoints the location (package manager is immutable)
• When updating, auto-propagates to all dependents (and their dependents, transitively) so they reference the new version
• Signature/definition change warnings: if a function's parameter types or return type changed (or a type's definition changed), prints
  a warning with old vs new and lists affected dependents for manual review
• Added undo command to step back one version at a time, reverting the associated propagation (with confirmation when dependents are affected)
• New PropagateUpdate and RevertPropagation ops to record what changed so it can be undone
• Added AstTransformer.fs to rewrite ASTs, swapping old UUIDs for new ones
• Added Propagation.fs for the core propagation algorithm (discovery, UUID mapping, transitive chain handling, mutual recursion)
• Handles edge cases: self-recursion, mutual recursion, diamond dependencies, cross-item propagation (type change affects fn), overlapping propagations during undo

[StachuDotNet]

Good work. I still have a general feeling/concern that the solution here is susceptible to sync-centric race conditions, and generally might be more complicated than we'd like. And it's a bit further committing to doing things in F#-land rather than Darklang land. But, it's a step in the right direction solving for a problem. We'll iterate here over time, for sure.