Type procs, functions, and TVFs as [Args, ReturnType] tuples

[damusix]

Summary

Procs, functions, and TVFs should be typed as tuples: [Args, ReturnType] instead of just Args.

Currently, the generic type maps only capture the input parameters:

type MyProcs = {
    get_users: { department_id: number };
    refresh_cache: void;
};

// Return type must be specified at every call site
const users = await ctx.proc<User>('get_users', { department_id: 1 });

Proposed: each entry becomes a tuple [Args, ReturnType]:

type MyProcs = {
    get_users: [{ department_id: number }, User];
    refresh_cache: void;  // shorthand for [void, void]
};

// Return type is inferred when the tuple provides it
const users = await ctx.proc('get_users', { department_id: 1 }); // → User[]

// But the generic is still available for overriding or ad-hoc calls
const users = await ctx.proc<SpecialUser>('get_users', { department_id: 1 }); // → SpecialUser[]
await ctx.proc('refresh_cache'); // → void

Rules

• SomeProc: [Args, ReturnType] — full tuple form
• If Args is empty/unused, use void → [void, ReturnType]
• If ReturnType is empty/unused, use void → [Args, void]
• Plain void (no tuple) is shorthand for [void, void] — no args, no meaningful return
• proc() and tvf() currently return T[] — with tuples, return becomes ReturnType[]
• func() currently returns scalar T — with tuples, return becomes ReturnType
• The T return type generic remains available — it defaults to the tuple's ReturnType but can be explicitly overridden at the call site

Behavior

1. Tuple provides return type, no generic specified → infer from tuple
2. Tuple provides return type, generic explicitly specified → generic wins (override)
3. No tuple / plain void → falls back to unknown (same as today), user specifies T manually
4. Ad-hoc / untyped calls → user can still call ctx.proc<MyType>(...) for procs not in the type map, or to override the mapped return type

Affected Surfaces

• Context class generics: Context<DB, Procs, Funcs, Tvfs>
• ctx.proc(), ctx.func(), ctx.tvf() method signatures
• createContext<DB, Procs, Funcs, Tvfs>() factory
• ImpersonatedScope<DB, Procs, Funcs, Tvfs> interface
• SDK type exports

Benefit

The type map becomes the single source of truth for both input and output shapes, eliminating repetitive annotations at call sites — while preserving full flexibility for ad-hoc calls and explicit overrides.