feat(share/eds): ODSReader

[distractedm1nd]

Should be based on top of #1232 if not already merged when started.

There needs to be an ODSReader that takes the reader returned by GetCAR and limits the reader to the CAR header and first quadrant (ODS). The reader returned by ODSReader should only truncate from the end - meaning that the CAR header included in the reader returned by GetCAR will be included.

The amount of blocks to be read from the CAR should be determined after reading the CAR header, which contains the number of roots found in the CAR. The length of the ODS can be calculated with this information. The implementation of ODSReader will probably be the most elegant using carv1.NewReader.