[ACP-194] update named-block label definitions

[ARR4N]

There has been some confusion about whether ACP-194 (a) modifies finality guarantees, and (b) forces users to wait until settlement (i.e. the safe block). Both of these are incorrect interpretations.

Having APIs support both the safe and finalized block labels, with the same meaning, contributed significantly to (a) because of the word finalized. As they were redundant, use of finalized is removed.

Concerns around (b) are clarified with an explanation of the meaning of safe (absolute and with respect to hard-drive corruption), with guidance on its usage and alternatives to achieve faster guarantees.

[StephenButtolph]

We had discussed this offline, but just to write it down: There is a pretty high probability that we'll need to support all of the labels for compatibility with standard ethereum tooling.

[ARR4N]

We had discussed this offline, but just to write it down: There is a pretty high probability that we'll need to support all of the labels for compatibility with standard ethereum tooling.

What do we want to do with "finalized" then? If we make it the same as "latest" then the ordering is different to what people expect. If it's an alias of "safe" (the natural definition in my opinion) then we have the same problem of people incorrectly thinking that "now Avalanche has 5s finality".

[StephenButtolph]

I think we will probably need to maintain the same ordering that tooling expects and just deal with any misconseptions that arise from it