migrator: typed: strict

[hyuraku]

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part of #17297

[Copilot]

Pull request overview

This PR upgrades the migrator.rb file from typed: true to typed: strict mode in Sorbet, adding comprehensive type signatures throughout the codebase as part of the ongoing effort to improve type safety (#17297).

Key changes:

• Added type signatures to all class methods, instance methods, and error class constructors
• Added type annotations for all attr_reader declarations
• Used T.let with explicit types for all instance variable initializations to satisfy strict mode requirements

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[MikeMcQuaid]

Thanks @hyuraku looking good so far! There's still a bunch of T.must (including those I didn't comment on) where I don't think there's a sufficient guarantee that it is non-nil. You can see a few examples I've provided to provide that guarantee.

[MikeMcQuaid]

@hyuraku A few more T.must to cleanup.

[MikeMcQuaid]

Looks great, thanks @hyuraku! One more tiny tweak.

[MikeMcQuaid]

Thanks @hyuraku!

[hyuraku]

@MikeMcQuaid
Tests seem to have been cancelled. Should I re-run them?