Support for Deepseek Harness

[TibixDev]

Deepseek Harness should be the best choice for Deepseek models, it has a rich plugin ecosystem so it should be easy to integrate perhaps with a plugin into T3Code?

[TibixDev]

This is also discussed in #7331

[MDHaarith]

Be cause my cache hit rate at lowest was 97.3% and the highest was 99.2% . But I use opencode-go subscription in dsh. It is a huge saving for me when I use a lot of token like 100M tokens a day. I really support the addition of DeepSeek harness.