add missing methods

[zevaverbach]

all of the /staking endpoints are not implemented. The withdrawal and saved addresses endpoints are, I think, purposefully omitted.

I've verified that the other categories of endpoints are present, haven't checked through all these yet:

orders
fills
funding payments
leveraged tokens
options

[zevaverbach]

@LeeChunHao2000 where did you find srm_stakes/unstake_requests/? It's not in the documentation currently.

[LeeChunHao2000]

Oh, FTX has changed srm_stakes/unstake_requests/ to /staking/unstake_requests

https://docs.ftx.com/#unstake-request