Rename the fields in ResumeClassifierBlockState

[V0ldek]

Is your feature request related to a problem? Please describe.
I just had to write this line of code:

block.block.block[block.idx] == b'"'

I think it's self explanatory. In more details, this stems from a couple of things.

1. We often use a variable representing either a QuoteClassifiedBlock or the ResumeClassifierBlockState as block (or b).
2. ResumeClassifierBlockState has the field that holds the QuoteClassifiedBlock and it's called block.
3. And that struct has a field holding the actual input block called block.

Describe the solution you'd like
Anything sensible here. My initial hunch is:

1. Rename such variables to block_state or resume_state or classifier_state.
2. Rename the first field to quote_classified or quote_classification.
3. As an alternative, leave that field as block but rename the one on QuoteClassifiedBlock to source.

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