Support checking for arbitrary options on .calls

Support checking for arbitrary options on .calls: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). I'm working on a Cloudflare Worker script that uses arbitrary options on a fetch call (as specified here). However, I'm unable to test if those options are set correctly because…

The task

I'm working on a Cloudflare Worker script that uses arbitrary options on a fetch call (as specified here). However, I'm unable to test if those options are set correctly because fetch-mock removes them from the options list (as seen here). Example:

Part of XiaomiMiMo/MiMo-V2.6-RL-oss.