Speed up override checks

What does this MR do and why?

Prefer method_defined? over instance_methods.include? (and friends).

Inspired by !103699 (comment 1169110599).

On my local machine I see the following results running hyperfine with bundle exec rake lint:static_verification lint:static_verification_with_database:

Before

$ hyperfine "bundle exec rake lint:static_verification lint:static_verification_with_database"
Benchmark 1: bundle exec rake lint:static_verification lint:static_verification_with_database
  Time (mean ± σ):     14.987 s ±  0.368 s    [User: 13.598 s, System: 0.853 s]
  Range (min … max):   14.588 s … 15.778 s    10 runs

After

$ hyperfine "bundle exec rake lint:static_verification lint:static_verification_with_database"
Benchmark 1: bundle exec rake lint:static_verification lint:static_verification_with_database
  Time (mean ± σ):     14.162 s ±  0.556 s    [User: 12.798 s, System: 0.803 s]
  Range (min … max):   13.324 s … 14.900 s    10 runs

How to set up and validate locally

time bundle exec rake lint:static_verification lint:static_verification_with_database

MR acceptance checklist

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