Fix projection drops member fields with field middleware

[PHILLIPS71]

Problem

SelectionExpressionBuilder.CollectSelection only projected fields with a pure resolver. Any middleware on a field removes its pure resolver, and one global UseField removes it from every field in the schema (ObjectField.IsPureContext).

With a global middleware registered, every selected field was silently dropped from QueryContext<T> and ISelection.AsSelector<T>() selectors. The builder fell back to the id-only selector (root => new Entity { Id = root.Id }), the database only fetched the id column, and every selected non-nullable field failed at runtime with HC0018. Nothing at schema build time or in the logs pointed at the middleware.

Fix

Purity decides how a field executes, not what data it needs. A member-bound resolver still reads the member when middleware wraps it, so the member still has to be projected. CollectSelection now accepts a field when its ResolverMember is declared on the parent runtime type, a base type, or an implemented interface. It no longer requires a pure resolver.

The other guards are unchanged. ResolveWith and extension resolvers stay excluded unless bound via [BindMember]. Method-inferred fields stay excluded by the PropertyInfo check. Connection and collection segment fields stay excluded.

One behavior change beyond the bug: member-declared fields with a custom Resolve(...) delegate now project the member even when the delegate is not pure. This over-fetches at most one column and never under-fetches. Pure custom delegates already behaved this way.

Test

GlobalFieldMiddlewareProjectionTests registers a pass-through UseField on a schema with a plain entity and asserts the captured selector binds the selected member. Without the fix the selector only binds Id and the request fails with HC0018.