fix(typescript): generate non-nullable json columns as NonNullable<Json>

[Maliik-B]

Problem

A NOT NULL json/jsonb column generates the TypeScript type Json, but the generated Json type is itself nullable:

export type Json = string | number | boolean | null | { [key: string]: Json | undefined } | Json[]

So the column type structurally permits null even though Postgres forbids it. Studio reports the column as non-nullable, but the generated types disagree.

Closes #1055.

Fix

generateNullableUnionTsType already special-cases unknown/any (which include null) by not appending | null. This applies the same reasoning to Json: a non-nullable json/jsonb column is narrowed to NonNullable<Json> so the type reflects the database constraint.

if (tsType === 'Json' && !isNullable) {
  return `NonNullable<${tsType}>`
}

Scope

• Only non-nullable json/jsonb columns change (Json becomes NonNullable<Json>). Nullable json columns are untouched, since Json already covers null.
• The change sits in the single nullability chokepoint, so it covers Row, Insert, and Update consistently. Function return types and composite-type attributes call this helper with isNullable: true, so they are unaffected. Array types ((Json)[]) are unaffected.

Tests

Added a regression test that spins up a throwaway schema with a NOT NULL jsonb column and a nullable jsonb column, generates types scoped to it, and asserts the non-nullable column is NonNullable<Json> while the nullable one stays Json | null. It follows the inline-schema pattern from the existing included/excluded-schemas test, so it adds no fixture churn to the shared snapshots.

Note on the type-generation extraction

I see #1084 and supabase/pg-toolbelt#302 are moving these templates into @supabase/postgrest-typegen. This patch targets typescript.ts here; happy to port the same one-line guard to the extracted package instead if that is the better home. @avallete