breaking!: rewrite fidget.nvim

[j-hui]

Gone is the old, single-file mess of a state machine. Here's some new features:

• Plays nice with Neovim's built-in LSP progress handler
  • No longer overriding the ["$/progress"] handler like the old implementation did
  • Compatible with both the 0.8.0-0.9.X handler and the one currently on nightly (i.e., to appear in 0.10.0)
• Support for vim.notify()-like interface
  • Support "notification groups", which can each have a separate configuration for things like highlights and icons (still supports animations, of course). Sorted according to priority.
  • Notification groups and items are indexed by user-specified keys, so updating/overwriting them is really easy.
  • Each LSP server can be configured with its own notification group.
• Explicit DOM/model for notifications subsystem
  • I can advance the state of the notifications model without worrying about rendering/textlock
  • Makes debugging and testing much easier (though a thorough test suite has yet to be implemented)
  • Should make cacheing renders easier, to avoid redrawing the terminal (though this is unimplemented so far)
• Synchronous execution model, i.e., "tick-driven"
  • The LSP progress and notification subsystems are running at independent rates and communicate asynchronously
  • Only poll when work needs to be done
  • Animations are much more stable (i.e., frames are always computed wrt synchronized wall clock time)
  • Rate-limiting/deliberate frame-dropping is theoretically possible
• Implementation is much more modular, configurable, and hackable
  • Options are now declarative, with the setup() function being constructed programmatically.
  • The structure of the options follows the structure of the implementations' modules; the two will hopefully keep each other sane and navigable.
  • A lot of modules have their members exposed publicly, so many more things beyond the setup options are technically overridable.

Yeah, some of these implementation decisions are questionable or over-engineered, but at least the code feels much more flexible and hackable now. I've added several features in the last couple of days that took little effort with the current design/organization.

[j-hui]

lol I can only link 10 issues at a time. software development practices at an all time low...

[j-hui]

Closes #99