embedding: add raw option for --embd-output-format (#16541)

embedding: add raw option for --embd-output-format (#16541)

* Add --embd-output-format raw for plain numeric embedding output

This new option outputs embeddings as raw space-separated floats, without JSON or 'embedding N:' prefixes. Useful for downstream vector pipelines and scripting.

* Move raw output handling into format handling section

* Move raw output handling into else-if block with other format handlers

* Use LOG instead of printf for raw embedding output

* docs: document 'raw' embedding output format in arg.cpp and README