Migrate kt tests off hamcrest

[jamesonwilliams]

Contributor checklist

• I am following the Code Style Guidelines
• I have tested my contribution on these devices:

• MacBook (unit tests)
• Pixel 8 API 34 emulator (connected tests)

• My contribution is fully baked and ready to be merged as is
• I ensure that all the open issues my contribution fixes are mentioned in the commit message of my first commit using the Fixes #1234 syntax

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Description

In #13884, I am migrating the remaining Java/Hamcrest tests to Kotlin/AssertK.

In this PR, I am migrating the remaining Kotlin/Hamcrest tests to Kotlin/Assert. There are uses of Hamcrest in both the unit and connected device tests. A good number of these are under-the-hood via helper functions in KotlinAssertsUtil.kt and TestUtils.kt.

To find the remaining Kotlin files that still use Hamcrest, I used:

 rg hamcrest $(git ls-files "app*.kt") $(git ls-files "*lib*kt")

And replaced every call site with the equivalent AssertK expression. (Frequently using a find/replace regex and then cleaning up by hand.)

Testing

./gradlew qa
[...snip...]
BUILD SUCCESSFUL in 3m 15s

./gradlew :Signal-Android:connectedPlayProdInstrumentationAndroidTest
[...snip...]

^ FixInAppCurrencyIfAbleTest fails; but it does without these changes, too. So, the results of the suite are unchanged, and the failure is not related to this set of changes.