fix(core): resolve compound primary key component metamodels to their columns

[zantvoort]

Problem

Per-component metamodels of a compound primary key (VetSpecialty_.id.specialtyId, Metamodel.of(VetSpecialty.class, "id.specialtyId"), and the leaves returned by Key#flatten()) fail template and predicate resolution with Column not found for metamodel, even though the generated metamodel classes expose these nodes. See #216 for the full analysis.

Root cause

ModelFactory#createColumns registers every component column of a record-typed @PK under the key's group metamodel (via the keyMetamodel override), so the column map carries no entry for the component's own canonical form. The component node is a scalar leaf, so the inline prefix fallback does not apply. Plain non-key inline records keep their own metamodels, which is why Owner_.address.city resolves while compound key components do not.

Fix

When the key's group metamodel overrides a component column's addressing identity, the component's own metamodel is retained as the column's secondaryMetamodel. ModelImpl#initColumnMap already indexes secondary metamodels (the mechanism foreign keys use for their referenced-PK mirror), so component lookups resolve without any change to the lookup path:

• getColumns(id.specialtyId) → the single component column,
• getColumns(id) → all key columns, exactly as before (the group registration is untouched),
• primary metamodel identity is unchanged, so PK-based WHERE compilation, value binding, and the ambiguity check are unaffected,
• depth-general: compound-PK components of foreign-key-expanded relations resolve too, since the retained metamodel carries the full path.

Tests

• ModelImplIntegrationTest#testVetSpecialtyCompoundPkComponentColumns: component lookups return their distinct single columns and the compound lookup still returns both.
• TemplatePreparedStatementIntegrationTest#testSelectCompoundPkComponent: a SELECT DISTINCT template using a component metamodel compiles and executes.

Full storm-core suite passes.

Fixes #216