Create a type to handle Rust's `f64` from the RPC server

[buffalojoec]

Motivation

Currently in the saga of the new (experimental) Web3 JS library, we've introduced the type U64UnsafeBeyond2Pow53Minus1, which aims to represent a Rust u64 while quite obviously stating this type's limitations.

We do not have such a type for Rust's f64, which is a return type used by many RPC methods in the RPC server.

Example use case

Two methods I've encountered will return one or more fields of type f64:

• getInflationGovernor
• getInflationRate

There are likely more.

Details

We should ideally craft a similar type to U64UnsafeBeyond2Pow53Minus1, so that it explicitly states the type's limitations, and perhaps as we move closer to release can iron this out - either by delving into the RPC server's code or our own.

Note: I am actively researching this, but throwing this flare up in case anyone has any immediate ideas!