Add constructor preserved block documentation

[christiane-certora]

to document https://github.com/Certora/EVMVerifier/pull/8117

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Jira ticket: TODO
Link to generated documentation: TODO

[johspaeth]

Tiny recomendation.

[johspaeth]

I think we can write this more explicit. Wdyt?

A method block with no method signature is called the generic preserved block. The generic preserved block is used for all methods that don't have a specific preserved block, including the fallback() method. Note, the generic preserved block is not applied for the induction base step, for the induction base step use preserved constructor instead.

[christiane-certora]

Very nice. I also updated the whole section to call it "generic" and not sometimes "default", since that just seemed inconsistent and confusing.