Support constructor registry in DynamicValue.toTypedValue for AST-rebuilt schemas (#511)

[chengdazhi]

/claim 511

Closes #511

Problem

When a schema is rebuilt from its AST (schema.ast.toSchema), records are materialized as Schema.GenericRecord, which only knows how to build a ListMap[String, _]. Converting a dynamic record with such a schema therefore yields a raw ListMap instead of the original case class — the typed constructor was lost when the schema was turned into a MetaSchema.

Solution

Implements the registry approach suggested by @jdegoes in the issue discussion (#511 (comment)):

• New overload DynamicValue.toTypedValue[A](registry: PartialFunction[TypeId, DynamicValue.Constructor[_]])(implicit schema: Schema[A]): Either[DecodeError, A].
• New DynamicValue.Constructor[A], which builds an A from the decoded field values of a record, with Constructor.fromSchema and Constructor.registry helpers to build a registry directly from record schemas (including the implicit derived ones, so no reflection is involved).
• The registry is threaded through the whole conversion, so records are reconstructed at any nesting level: nested records, Option, sequences, sets, maps, Either, tuples and enum cases — not just at the top level (this is where the naive attempt in dynamic value to typed using a registry #725 stops).
• Records missing from the registry keep the existing behaviour and decode to their generic representation (ListMap[String, _]), so the change is fully backwards compatible; decodeStructure retains its original signature.

Usage with the reproduction from the issue:

final case class User(name: String, age: Int)
implicit val schema: Schema[User] = DeriveSchema.gen[User]

val user        = User("John", 30)
val userDynamic = schema.toDynamic(user)
val registry    = DynamicValue.Constructor.registry(schema)

userDynamic.toTypedValue(registry)(schema.ast.toSchema)
// Right(User("John", 30))

Tests

• 5 new tests in DynamicValueSpec covering: top-level records rebuilt from their AST, fallback to generic records when no constructor is registered, nested records / Option / Chunk, enum cases, and failure when the dynamic record does not match the registered constructor.
• Verified locally: zioSchemaJVM/test, zioSchemaDerivationJVM/test, testsJVM/test on Scala 2.12.21, 2.13.18 and 3.3.8; zioSchemaJS/test, testsJS/testOnly zio.schema.DynamicValueSpec on 2.13.18; zioSchemaNative/compile, testsNative/compile; scalafmtCheckAll, scalafix --check on the touched modules; zioSchemaJVM/mimaReportBinaryIssues (no problems).

Note: this PR was prepared with the assistance of an AI coding agent; the changes were reviewed and verified by running the checks listed above.

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