Group JSON ingestion schema state

[jwils]

Why

Keep JSON ingestion-specific schema definition state off the shared SchemaDefinition::State surface. This follows up on #1259 by grouping the extension state behind one accessor.

What

• Add JSONIngestionState and attach it via State#json_ingestion_state
• Move JSON schema config and deprecated-element registries into the contained state
• Update typed helpers, specs, doctests, and schema test support to use the contained state

Risk Assessment

Low — internal schema-definition state refactor; public DSL behavior remains unchanged.

References

• Stack Info: Stacked on Move deprecated schema markers to JSON ingestion #1259
• Follow-up to Move deprecated schema markers to JSON ingestion #1259 (comment)

Validation:

• script/lint --fix
• script/spellcheck -w
• script/type_check
• RUBYOPT=--disable-frozen-string-literal bundle exec rake site:doctest
• bundle exec rspec elasticgraph-json_ingestion/spec/unit/elastic_graph/json_ingestion/schema_definition/deprecated_element_spec.rb elasticgraph-json_ingestion/spec/unit/elastic_graph/json_ingestion/schema_definition/json_schema_spec.rb elasticgraph-json_ingestion/spec/unit/elastic_graph/json_ingestion/schema_definition/indexing/json_schema_with_metadata_spec.rb
• script/run_gem_specs elasticgraph-json_ingestion
• Not fully run locally: script/run_gem_specs elasticgraph-schema_definition and script/quick_build; local datastore boot is blocked because Docker is not running (~/.docker/run/docker.sock is unavailable).
• Attempted RUBYOPT=--disable-frozen-string-literal bundle exec rake site:validate; the CI-relevant doctest failure is fixed, but local execution later stops in site:npm_install with an npm dependency resolution issue.