Validate against all loaded namespaces via a namespace-aware dispatcher (fixes #608)

[rly]

Problem

Directly addresses #608. Validation assumes a single namespace: ValidatorMap is built from one SpecNamespace and its get_validator raises when a builder's type is not in that namespace. A file's builder tree is validated against one namespace at a time, so a file that uses two independent extension namespaces fails.

Reproduction

A file whose root type comes from one extension and a child from another (e.g. ndx-multisubjects root NdxMultiSubjectsNWBFile + an ndx-sound AcousticWaveformSeries stimulus) raises during validation:

ValueError: data type 'NdxMultiSubjectsNWBFile' not found in namespace ndx-sound

This reproduces via pynwb.validate(path=...) (pynwb picks the "most specific" leaf namespaces and validates the whole tree against each) and is independent of nwbinspector. #608 also describes a related false-negative: a subtype defined in one extension namespace placed where its parent type is expected is wrongly rejected.

Design: a namespace-aware dispatcher (not a merged bare-name registry)

A file can legitimately contain two different types that share a name, defined in two independent namespaces. HDMF's read/construct path already differentiates them: every typed builder stores a namespace attribute and is resolved by (namespace, data_type) (TypeMap.get_cls → get_builder_ns + get_dt_container_cls(dt, ns)). Validation must do the same. Merging all namespaces into one registry keyed by bare name would collapse distinct same-named types and misdispatch, so that approach is rejected.

Instead, validate the whole builder tree in one pass with a dispatcher that:

• For each builder, reads its (namespace, data_type) from its attributes and resolves the validator from that namespace's ValidatorMap (each namespace's catalog is self-contained: its own types plus its transitively-included dependencies). Root (ndx-multisubjects, …) → ms validator; child (ndx-sound, …) → sound validator. This fixes the crash.
• Resolves the Account for all loaded namespaces during validation #608 subtype false-negative by matching a child against a spec via the child's hierarchy computed in the child's own namespace (required_type_name in child_hierarchy), rather than enumerating subtypes of the required type across namespaces. This is collision-safe because a cross-namespace match only succeeds through a shared dependency type (the same type identity, not a name collision).
• Routes the reference-validation reach-throughs (currently self.vmap.namespace.catalog.get_spec(...) / self.vmap.namespace.get_hierarchy(...) in AttributeValidator and DatasetValidator) so a referenced builder's hierarchy is computed in the referenced builder's own namespace, read from its namespace attribute.

Why not bare-name merging

Bare-name lookups across namespaces assume a name identifies the same type everywhere. That holds for shared dependencies (e.g. core VectorData) but not for independent leaves that reuse a name for different types. Dispatching by the builder's stored (namespace, data_type) keeps resolution namespace-scoped and mirrors the proven construct path.

Depends on

• Add namespace-agnostic type resolution to NamespaceCatalog (get_spec/get_hierarchy/get_subtypes across all namespaces) #1528 / Add namespace-agnostic type resolution to NamespaceCatalog (#1528) #1531 provide NamespaceCatalog conveniences and type_key/type_keys. The dispatcher primarily relies on the existing two-argument get_spec(namespace, data_type) / get_hierarchy(namespace, data_type) and get_namespace(name), using the namespace read from each builder.

Acceptance criteria

• A file rooted in one extension namespace with a child from an independent extension namespace validates without a "not found" error.
• A subtype defined in a sibling namespace is accepted where its parent type is expected; an unrelated type still errors.
• Two different types that share a name across namespaces are each validated against their own spec (no misdispatch).
• New multi-namespace tests in tests/unit/validator_tests/test_validate.py.

Note on in-flight work

PRs #1480 (ValidationResult wrapper) and #1443 touch the validator return path and overlap with this change. Sequence after those land or coordinate to avoid conflicts.

The pynwb consumer (pynwb/src/pynwb/validation.py: drop the leaf-namespace selection, validate once via the dispatcher) is a follow-up in the pynwb repo.