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

examples/embedding/README.md

@@ -38,6 +38,7 @@ The above command will output space-separated float values.
 |            | multiple embeddings          | $[[x_1,...,x_n],[x_1,...,x_n],...,[x_1,...,x_n]]$
 | 'json'     | openai style                 |
 | 'json+'    | add cosine similarity matrix |
+| 'raw'      | plain text output            |
 
 ### --embd-separator $"string"$
 | $"string"$   | |