Integrate the page cache hashtable during __page_read, including:

1. Lookup the hashtable before sending the request to the block manager.
2. Cache the disk image when it is returned by the block manager.

The current POC has partially completed the code, this ticket is to cherry pick or copy the code snippet from the POC branch, then clean up the code, add necessary logging and failing messages. This ticket depends on the implementation of hashtable get/put/insert functions.