fix: serialize Date objects inside repeated nodes

[fhgffy]

Scalar Date values are serialized as text, but dates in an array go through object recursion and become empty tags. This also prevents tagValueProcessor from receiving those values.

Keep Date array entries on the existing text-value path. The regression checks scalar/array consistency, custom processing, and oneListGroup output.

Validation:

• All three new regressions fail on the base revision.
• npm test: 139 specs, 0 failures, 1 existing pending spec.
• npm run bundle: both bundles compile; source ESM and rebuilt CommonJS retain Date text and apply custom processing.
• The new spec passes ESLint. Direct source lint reports the same four pre-existing errors as the base revision.

The existing lint script references an absent benchmark directory, and test-types references an absent spec/typings/typings-test.ts.