livecheck: expand typed: strict usage

[samford]

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This updates livecheck files to use typed: script where feasible.

The remaining exception is livecheck/strategy.rb, as I wasn't able to figure out how to resolve the typing issues around the @strategies variable (I tried a couple of approaches but couldn't find a working solution):

livecheck/strategy.rb:100: Use of undeclared variable @strategies https://srb.help/6002
     100 |        return @strategies if defined? @strategies
                         ^^^^^^^^^^^
  Note:
    Use T.let to declare this variable.
    For more information, see https://sorbet.org/docs/type-annotations

livecheck/strategy.rb:102: The instance variable @strategies must be declared using T.let when specifying # typed: strict https://srb.help/7043
     102 |        @strategies = {}
                  ^^^^^^^^^^^
  Autocorrect: Use -a to autocorrect
    livecheck/strategy.rb:102: Replace with T.let({}, T.nilable(T::Hash[T.untyped, T.untyped]))
     102 |        @strategies = {}
                                ^^

livecheck/strategy.rb:100: Use of undeclared variable @strategies https://srb.help/6002
     100 |        return @strategies if defined? @strategies
                         ^^^^^^^^^^^
  Note:
    Use T.let to declare this variable.
    For more information, see https://sorbet.org/docs/type-annotations

livecheck/strategy.rb:102: The instance variable @strategies must be declared using T.let when specifying # typed: strict https://srb.help/7043
     102 |        @strategies = {}
                  ^^^^^^^^^^^
  Autocorrect: Use -a to autocorrect
    livecheck/strategy.rb:102: Replace with T.let({}, T.nilable(T::Hash[T.untyped, T.untyped]))
     102 |        @strategies = {}
                                ^^

This includes changes to resolve the other type errors in strategy.rb but leaves the file as typed: true for now.

Related to #17297.

[MikeMcQuaid]

Thanks again @samford!