Exclude sealed marker types from TypeScript output

[almarzn]

Summary

Adds support for excluding sealed interface/class markers from generated TypeScript output.

Problem

When using sealed interfaces to organize a type hierarchy, intermediate sealed types that don't have @JsonSubTypes were being generated as TypeScript interfaces and included in unions, even though they serve only as grouping markers.

Example:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "unit")
public sealed interface Quantity {
    sealed interface DecimalAmount extends Quantity {  // marker, no @JsonSubTypes
        record Gram(BigDecimal amount) implements DecimalAmount {}
        record Kilogram(BigDecimal amount) implements DecimalAmount {}
    }
    record Unspecified(String notes) implements Quantity {}
}

Before this change:

interface Gram extends DecimalAmount { ... }
interface DecimalAmount extends Quantity { ... }  // unwanted
interface Quantity { ... }
type QuantityUnion = Gram | Kilogram | ... | DecimalAmount;  // marker in union

After this change:

interface Gram extends Quantity { ... }  // extends root directly
interface Quantity { ... }
type QuantityUnion = Gram | Kilogram | ... | Unspecified;  // no marker

Solution

Added excludeSealedMarkerTypes() transformation in ModelCompiler that:

1. Identifies sealed types without @JsonSubTypes or @JsonTypeInfo as markers
2. Removes them from the model
3. Replaces parent/extends references to markers with the marker's parent
4. Expands markers in tagged unions to their permitted subclasses

Changes

• ModelCompiler.java: Added excludeSealedMarkerTypes(), isSealedMarker(), getSealedPermittedSubclasses(), findNonSealedParent()
• TsBeanModel.java: Added withParent() method
• SealedInterfaceTest.java: Added test for sealed marker exclusion

Testing

• New test SealedInterfaceTest.testSealedInterfaceMarkerExcluded() passes
• All 378 existing tests pass