Refactor indexing

[tkporter]

Description

• Stops creating a new client a bunch of times in rpc.rs (I haven't yet changed grpc.rs - this is because the client's functions are &mut self, so will have to think about what to do here)
• Changes unwrap_or_none_result to not include the let Some(varname) bit so we can do let varname = unwrap_or_none_result!(...)
• Instead of a get_parser(&self, ...) fn that returns a closure, we just pass a the function Self::[data_type]_parser
• Refactors these parsers to be a bit more defensive - e.g. each param is represented as an Option so it's clear if one isn't parsed, and we also get the _contract_address param (which is auto-set by the cosmwasm runtime). It returns a ParsedEvent<T> so that we can return the _contract_address in there too
• Refactors the range indexing in rpc.rs, including an important fix to ensure that the contract address of an event is the one we actually want to index

Drive-by changes

n/a

Related issues

n/a

Backward compatibility

Fully

Testing

Unit tests, ran locally