Fix autocomplete issues in bindings crate

[coolreader18]

Description of Changes

Fixes 2 specific issues:

• invalid syntax (namely, at least, an incomplete if block: if foo) in a reducer body would cause autocomplete to break.
  • This is fixed by upgrading the proc-macro2 dependency.
• No completions for methods on unique columns.
  • This is fixed by fiddling around with the bounds on the impl block for UniqueColumn. Best I can tell is that this was hitting some poorly-handled edge case in chalk, related to evaluating bounds that are too dependent on each other (?)

Expected complexity level and risk

1

Testing

• Both cases now provide autocomplete with rust-analyzer.

[gefjon]

🙏 thank you so much for figuring this out.