Validate property values on export to prevent writing invalid files

[ehennestad]

⚠️ Depends on — merge these first:

• fix: export scalar datetime as a scalar dataset #835
• Add context-aware schema violation reporting #836

Motivation

MatNWB validates property values in property set method when objects are constructed, but export does not re-validate them before writing to file. This was sufficient while the only way to populate a property was through its (strict) setter.

PR #822 introduced permissive reads for DynamicTable column names, and the broader read-validation work in #776 will extend permissive reads to other schema checks (data type, shape, neurodata type, fixed/constant attribute values). Once a value can enter an object without passing strict validation, nothing stops it from being written back out to a new, non-conforming file.

This PR adds an export-time guard so a value that bypassed strict validation cannot be written to a new file.

Changes

• Add types.untyped.MetaClass/validateProperties, invoked in export alongside the existing required-property and custom-constraint checks. For each set property that has a generated validate_<prop> method, it re-runs the validator and discards the result, so there are no setter side effects such as type coercion or column-name syncing. If the value is invalid it raises NWB:Export:InvalidPropertyValue, including the property name and file location, and preserves the original validator error as a cause.
• Empty/unset optional properties are skipped, matching what export writes.
• Validators run in the default (strict) context here, so a schema violation is an error on export even when the same check is lenient during a read.

Relationship to other work

This is the write-side counterpart to the read-side permissiveness in #776 — read lenient (warn, keep value), write strict (error). It generalizes the pattern already used for DynamicTable (checkConfig via the custom-constraint path) to all property validators. Its user-visible effect lands together with #776, so this is best reviewed and merged alongside that work.

How to test

tests.unit.types.MetaClassValidatePropertiesTest exercises the guard with a small MetaClass test double: an invalid property value raises NWB:Export:InvalidPropertyValue with the property name, location, and original cause; an unset (empty) property is skipped; a valid value passes.

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

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[codecov]

Codecov Report

❌ Patch coverage is 97.14286% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (fix-scalar-datetime-export@f953063). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
+types/+untyped/MetaClass.m	97.14%	1 Missing ⚠️

Additional details and impacted files

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##             fix-scalar-datetime-export     #832   +/-   ##
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