fix: use vscode's inlay hint colors

[uncenter]

See https://github.com/catppuccin/vscode/blob/7b0ff73aa9e9718cbe418a3f90f771aa14a655b8/packages/catppuccin-vsc/src/theme/uiColors.ts#L181-L186. Left the background as mantle still, though in VS Code it is mantle with a 75% opacity - I don't think Helix supports hex colors with opacity at the end.

[uncenter]

Oh, and this would supersede #51 I guess.

[nik-rev]

What about blending mantle with base such that it looks as if the background color of the inlay hints was at 75% opacity?, e.g. "fake opacity"

[backwardspy]

i've been slow on this PR as i want to examine how we colour inlay hints/virtual text across all catppuccin ports, i'm not entirely happy with what vscode does for this at the moment. i think the type inlay hints are good, but some of the others such as elided lifetime hints in rust are quite hard to read.

i'm also not a fan of the darker background on inlay hints, it looks weird to me, but i think that parts quite subjective so i'll likely drop it if the majority prefer it this way.