* new payment driver: update deps & remove zksync
* new payment driver: initial integration
  * temporary fix of payment example -- will not work with new driver. TODO: make the new driver work in the example.
  * cleanup transfer, remove _transfer, remove gasless.
  * general way to compute chain_id based on config-payments.toml.
  * remove lots of code made obsolete by the new driver.
  * introduce signer for signing transactions for erc20_payment_lib
* temporarily disable payment fund.

---------

Co-authored-by: scx1332 <[email protected]>

This test used a serde_json::Value -> flexbuffers -> Rust struct serde
trip which is not guaranteed to work and should not be relied upon. The
proper route is Value -> flexbuffers -> Value -> Rust.

This only broke recently because without the arbitrary_precision feature
of serde_json the shorter path works. The feature has been enabled due
to the addition of erc20_payment_lib to the dependency graph, which
transitively depends on serde_json with arbitrary prec. Note that cargo
unifies duplicate dependencies under the assumption that features are
purely additive, hence the spooky action at a distance.