fix: ignore irrelevant warnings when reducing

[0marperez]

Issue #, if available:

Description of changes:

ProGuard encounters some warnings when reducing DynamoDB mapper that are safe to ignore, otherwise they fail the reduction tasks.

- dontwarn("org.gradle.internal.impldep.**") — suppresses warnings from Gradle internal implementation dependency classes
- dontwarn("module-info") — suppresses warnings from multi-release JAR module-info class files (Java 9+ module descriptors)
- dontwarn("org.gradle.kotlin.dsl.**") — suppresses warnings from Gradle Kotlin DSL internals

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