Schema export: publish config key to KV config field name mapping

[ncoghlan]

There are two essential formats for model and prediction configuration information:

• the flat key-value types used at the SDK boundary (LlmPredictionConfig, LlmLoadModelConfig, EmbeddingLoadModelConfig)
• the field listing based KvConfigStack format used in the LM Studio wire format

lmstudio-js defines the mapping between the two in https://github.com/lmstudio-ai/lmstudio-js/blob/main/packages/lms-kv-config/src/schema.ts

The lmstudio-js JSON schema export publishes both the SDK boundary types and the wire format types, but it doesn't publish the details of how to translate between them. Accordingly, lmstudio-python has to define its own duplicative mapping logic in https://github.com/lmstudio-ai/lmstudio-python/blob/main/src/lmstudio/_kv_config.py

This can lead to functionality lags, as the Python SDK may silently fail to translate defined-but-not-yet-implemented config settings from the SDK boundary formats to the wire config stack format.

Information which the Python SDK needs for each input key:

• the mapped config stack field name for the setting (both the namespace prefix, and the key name itself, since the latter may differ from the input attribute/key name)
• whether the value should be sent to the server as is, or if it should be nested as a checkbox subfield (that is, sent as {"key": server_config_name, "value": {"checked": True, "value": value}} rather than as just {"key": server_config_name, "value": value})

(corresponding lmstudio-python issue to consume the exported data file once it is available: lmstudio-ai/lmstudio-python#32