Release langchain-groq==0.1.6

Changes since langchain-groq==0.1.5

groq[patch]: Release 0.1.6 (#23655)
openai, anthropic, ...: with_structured_output to pass in explicit tool choice (#23645)
standard-tests: add test for structured output (#23631)
partners[minor]: Fix value error message for with_structured_output (#22877)
openai[patch], standard-tests[patch]: don't pass in falsey stop vals (#23153)
standard-tests[patch]: Update chat model standard tests (#22378)
docs: Standardize ChatGroq (#22751)
groq[patch]: add usage_metadata to (a)invoke and (a)stream (#22834)
multiple: implement ls_params (#22621)
multiple: add stop attribute (#22573)