Question : how to random access or skip during decryption

### Problem:

I have a need to handle large files and service a random address range for decryption.
Looking throgh the exampes I dont see an effecient way to do this.
It seems that the underlying encryption data is framed, but the CryptoInputStream doesn't skip in an input stream, and there isnt a support for a Readable Channel that I am aware of

### Solution:
With the existing API - I could use skip in the InputStream, but this will (as I see it) decrypt and throw away the skipped bytes, with extra I/O and CPU load
With an enhanced implementation we could skip on the input stream to the start of a frame and then decrypt that frame (skipping internally to the offset needed by decodng and thowin a few bytes if needed)

### Out of scope:

Start with the existing CryptoInputStream API and its framed encryption input behavior, then compare InputStream.skip with the requested Readable Channel support. Done means a caller can service a random address range by seeking to the relevant frame and avoiding decryption and I/O for discarded bytes.

Written by the indexing model from the issue text.