gpt-oss: implement harmony parsing (#15181)

gpt-oss: implement harmony parsing (#15181)

* model : add harmony parser for gpt-oss

* gpt-oss : fix grammar trigger from causing empty stack

* gpt-oss: tweak the grammar trigger again

* gpt-oss : add support for recipient in role header

* gpt-oss : fix ungrouped tool calls in grammar

* gpt-oss : loosen function name matching during parse

* gpt-oss : clean up workarounds

* gpt-oss : add template tests

* gpt-oss : simulate thinking and tool call tags

* gpt-oss : undo think tags when reasoning_format is none

* gpt-oss : set special tokens back to user defined

* gpt-oss : update openai-gpt-oss template

* server : filter out harmony thought messages

* gpt-oss : simplify parsing