feat(models): complete 1:1 OpenAI API surface + unified router #48

Job	Run time
native-backend/stable	34s
format/stable	24s
Pass MSRV values to other jobs	4s
clippy/stable	24s
cross_test/s390x-unknown-linux-gnu/stable	1m 31s
cross_test/i686-unknown-linux-gnu/stable	1m 33s
nostd/thumbv6m-none-eabi/stable	26s
miri	0s
cargo-careful	0s
docs/nightly	0s
blas-msrv	57s
tests/stable	1m 29s
tests/1.64.0	1m 17s
tests/beta	1m 28s
conclusion	0s
	10m 7s

Provide feedback