fix(types): make partial configs portable

[oriori1703]

Summary

• replace LuaLS-specific empty-table partial inheritance with explicit optional field overrides
• preserve strict internal configuration types and nested partial types
• make partial configuration annotations work in both LuaLS and EmmyLua

Verification

• every inherited strict field is represented in its partial class
• user configuration passes EmmyLua 0.25.1 and LuaLS 3.19.1 without missing-field diagnostics
• invalid partial values are still rejected by both analyzers
• strict configurations still report missing fields
• StyLua and git diff --check pass

Closes #2648

[saghen]

This type of operation is quite common in the neovim plugin space. I'd prefer that the new LSP support it, rather than having every plugin provide duplicated types that may drift out of sync.

[oriori1703]

This type of operation is quite common in the neovim plugin space. I'd prefer that the new LSP support it, rather than having every plugin provide duplicated types that may drift out of sync.

yeah, the duplication also bothers me (though as a user of the plugin the warning bother me a bit more :)

Unfortunately the intended way to do it in emmylua (using Partial<T>) is not supported in lua_ls.
Also it seems like emmylua is not intending to support the lua_ls way according to EmmyLuaLs/emmylua-analyzer-rust#871 and EmmyLuaLs/emmylua-analyzer-rust#328