dataconnect: modernize tests in ProtoStructDecoderUnitTest.kt, ProtoStructEncoderUnitTest.kt, and TimestampSerializerUnitTest.kt

[dconeybe]

The main changes are replacing Truth and assertThrows with kotest assertions (https://kotest.io/docs/assertions/assertions.html) and using kotest property testing (https://kotest.io/docs/proptest/property-based-testing.html) instead of hand-picking example values. Future PRs will modernize other tests.

[github-actions]

Release note changes

No release note changes were detected. If you made changes that should be
present in the next release, ensure you've added an entry in the appropriate
CHANGELOG.md file(s).

[github-actions]

Unit Test Results

  48 files  ±  0    48 suites  ±0   1m 27s ⏱️ +4s
478 tests  -   6  477 ✔️  -   7  1 💤 +1  0 ❌ ±0 
956 runs   - 12  954 ✔️  - 14  2 💤 +2  0 ❌ ±0 

Results for commit 7c1c1ee. ± Comparison against base commit bb5a4d4.

This pull request removes 10 and adds 4 tests. Note that renamed tests count towards both.

com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can decode a Struct with extreme Double values
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can decode a Struct with extreme Int values
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a complex object A
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a complex object B
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a complex object C
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a list of nullable Unit ending in Unit
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a list of nullable Unit ending in null
com.google.firebase.dataconnect.ProtoStructEncoderUnitTest ‑ encodeToStruct() should support OptionalVariable Value when T is nullable and null
com.google.firebase.dataconnect.ProtoStructEncoderUnitTest ‑ encodeToStruct() should support OptionalVariable Value when T is nullable but not null
com.google.firebase.dataconnect.ProtoStructEncoderUnitTest ‑ encodeToStruct() should support nested composite types

com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a list of non-nullable Unit
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode a list of nullable Unit
com.google.firebase.dataconnect.ProtoStructDecoderUnitTest ‑ decodeFromStruct() can encode and decode complex objects
com.google.firebase.dataconnect.ProtoStructEncoderUnitTest ‑ encodeToStruct() should support OptionalVariable Value when T is nullable

♻️ This comment has been updated with latest results.