Make the internal helper types of the typings internal

[lehni]

The ES module typings of 4.0 export what they declare export, while the 3.x namespace exported every type. The helper types added for the relation expression parser, the withGraph*() narrowing and the property names aren't meant for users, and are no longer exported:

• Whitespace, Trim, CountChar, IsBalanced, SplitList, ParseRelationList, ParseRelationString, RelationName, RelationNode, ParseRelationObject
• WithGraph, WithGraphProperty
• OptionalInsertPropertyNames, InsertablePropertyNames, RelationPropertyNames, InsertableGraphField, InsertableGraphReference, TypedRelationMappingFor, TypedModelClassSpecifier, PartialModelProps

The unused ItemType is removed. ParseRelationExpression, WithGraphRelations, FetchedRelations, UnnarrowedMethods, WithGraphTreeQueryBuilder and WithResultKind stay exported, as the declarations of inferred withGraph*() queries name them.

The internal checks have consistent names: UnknownExpressionModifiers, ShouldCheckModifiers, HasOnlyLiteralKeys, which also replaces four inline string extends keyof checks, IsSelectAll and HasModels.

Check time

pnpm bench:typings, against next: unchanged.

Tests

No type changes apart from the exports: the declarations emitted for a corpus of inferred queries, in loose and strict mode, are the same, with the removed types written out where they were named. pnpm test:typings passes with TypeScript 7 and 5.8.3.