chore: [ANDROSDK-2341] tidy up code after model migration

[taridepaco]

Cleans up leftovers from the migration of the Java models to Kotlin data classes. Guard clauses in the DTO mappers are normalized so that a single nullable check uses ?.let instead of an if/else null block, and every non-null assertion that the compiler proves redundant is removed across main, unit test and instrumented test sources. Removing an assertion or a safe call changes the type of the surrounding expression, so the pass was repeated until no warnings were left; the dead code this exposed (pointless let wrappers, unreachable elvis branches and a redundant == true) is cleaned up as well. A few var declarations that are never reassigned, also inherited from the Java conversion, become val.

Assertions that are still needed are untouched, and there is no behavior change: all of these are no-ops the compiler already optimizes away. Note that apiCheck currently fails on develop as well, unrelated to this branch, because the Koin compiler plugin emits org.koin.plugin.hints.* classes that are missing from the committed API dump; that drift is left for a separate ticket rather than folded in here.

Related task: ANDROSDK-2341

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
77.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud