Support enable-per-pid-reader and min-sequential-read-size-mb to accelerate mmap reads

[wlhee]

Description

Support enable-per-pid-reader and min-sequential-read-size-mb to accelerate mmap reads.

1. For each file handle, creates per pid GCS reader stream and stats (start, limit, read bytes count), so that each pid can seek forward and backward independently without interfering with each other
2. Allow configuring the minimum sequential-read-size-mb so that each GCS stream can have a minimum bytes that it can support.
3. This PR firstly refactored the random_reader to move all the GCS reading logics from randomReader to objectRangeReader so that each pid can have its own objectRangeReader and use it indepently.

Initial manual results show it reduced loading time from 13mins to 1min by setting perPidReader: true and minSequentialReadSizeMb: 200

Before:

After:

Link to the issue in case of a bug fix.

#2828

Testing details

1. Manual - NA
2. Unit tests - TODO
3. Integration tests - TODO

[wlhee]

Note: I haven't added flags or tests. Sent out this PR first to get early feedback.