Add direct result consumption

[eosobande]

Summary

• Add direct consume-once access through ResultConsumer.consume(key).
• Add PendingResult.Missing and PendingResult.Value.
• Keep the callback-based consumption API.
• Distinguish a missing result from PendingResult.Value(null).
• Update the public API declarations and documentation.
• Add the 0.2.0 changelog entry.

Usage

when (val result = resultConsumer.consume(resultKey)) {
    PendingResult.Missing -> Unit
    is PendingResult.Value -> handleResult(result.value)
}

The result remains consume-once. The first direct or callback consumer removes it from the store.

Validation

• Android unit tests passed.
• iOS simulator tests passed.
• API compatibility checks passed.
• Kover line and branch coverage checks passed at 100%.
• The full check, apiCheck, and koverVerify tasks passed.
• Sample tests and Android assembly passed.

Review

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