feat: add dependentSchemas keyword handler

[HasinAmir]

What this does

Implements the missing dependentSchemas keyword handler in processAST.ts.

Problem

The dependentSchemas handler was commented out, causing the fallback
handler to trigger with " This keyword handler is not implemented yet!"
for any schema using this keyword.

Solution

After inspecting the AST, I found Hyperjump compiles dependentSchemas
as an array of [propertyName, schemaUri] tuples , same shape as
patternProperties. The handler iterates these tuples and calls
processAST for each, creating child nodes labeled
dependentSchemas["propertyName"] connected to the parent.

Testing

Tested locally with a schema using dependentSchemas ,child nodes
render correctly with edges connecting to the parent.