feat(node): update node-offline chainfile sync for n3

[spencercorwin]

Description of the Change

• Updates chainfile sync and chainfile dump with "write start" and "read start". We now have the option to write/read the start block of the chainfile with the first four bytes. So it's possible that a chainfile has the start index instead of just the count first instead of the number of blocks. This allows for that now.

Test Plan

Tested manually. Works.

Alternate Designs

None.

Benefits

Proper chainfile sync/dump in N3.

Possible Drawbacks

None.

Applicable Issues

#2410
#2157