fix: extra byte read from chunk transfer

[xinsong-cui]

Issue #

Description of changes

Adds a public property contentBytesTransferred to track the content bytes transferred, excluding chunk metadata (need to opt in internal api to access).
This allows monitor file transfer progress without counting the overhead bytes from chunk encoding.

example usage:

override fun read(sink: SdkBuffer, limit: Long): Long = delegate.read(sink, limit).also {
    if (it > 0L) {
        val bytesTransferred = chunkedSource?.contentBytesTransferred ?: it
    }
}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

Affected Artifacts

Changed in size

Artifact	Pull Request (bytes)	Latest Release (bytes)	Delta (bytes)	Delta (percentage)
aws-signing-common-jvm.jar	72,447	71,836	611	0.85%