feat(core): implement Thing-level data schema mapping extraction

[siddharthbaleja7]

Fixes #1411

This PR implements the experimental nw:dataSchemaMapping feature at the Thing-level, allowing developers to extract specific nested values from Thing responses using dot-notation or JSON pointers.

As discussed with the maintainers, this feature strictly targets Thing responses (readProperty, invokeAction outputs, and subscribeEvent emissions). Input payloads are unaffected.

Key Implementation Details:

• Order of Operations: Extraction occurs after content deserialization but before JSON Schema validation inside interaction-output.ts.
• Servient-Level Injection: Added dataSchemaMapping to the Servient configuration. If a consumed/produced Thing Description lacks a mapping, the Servient's default mapping is automatically injected.
• Typings: Added @experimental tags to all nw: prefixed types in thing-description.ts.
• Zero Dependencies: Parsing logic is isolated inside helpers.ts without relying on external libraries.
• Strict Typing: All type casting is safely handled natively without relying on eslint-disable any casting.

Testing

• Added 20+ Unit Tests in server-test.ts and client-test.ts verifying extraction logic, overriding precedence, and error handling.
• Ran and passed all 136 core tests (npm run test -w packages/core).
• Passed extreme strict verification (npm run lint --workspaces and npm run test:browser locally).

Documentation

• Added an "Experimental Features: Data Mapping per Thing" section to the main README.md.

[danielpeintner]

I have some minor comments/suggestions.
Please let me know whether they make sense..

[danielpeintner]

Minor: I wonder whether we should keep the order of the arguments more consistent..
In handleActionInteractionOutput(...) we used to have synchronous after mapping. We could do the same here

[relu91]

@danielpeintner done, if everything looks good, please go ahead and merge this.

[danielpeintner]

Thanks @siddharthbaleja7 @relu91