feature: replace `github.com/invopop/jsonschema` with `github.com/google/jsonschema-go`

[alexandear]

Problem Statement

The current implementation uses github.com/invopop/jsonschema for JSON schema generation, which has an indirect dependency on github.com/mailru/easyjson. According to this analysis, easyjson is under sanctions, which creates compliance and security concerns for projects using it transitively.

Proposed Solution

Replace github.com/invopop/jsonschema with github.com/google/jsonschema-go/jsonschema, Google's official JSON Schema package for Go.

Key benefits of this migration:

• Zero dependencies.
• Maintained by Google as announced in their official blog post
• Reduced supply chain risk.