Buffer writes to block size

[akharit]

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This checklist is used to make sure that common guidelines for a pull request are followed.

Description of the change

Write was copying all data given to it. This can cause memory issues if the data to be written is large enough. Buffered the writes to block size.

General Guidelines

• The PR has modified HISTORY.rst with an appropriate description of the change and a version increment.
• The PR has supporting test coverage that confirm the expected behavior and protects against regressions, including necessary recordings.
• Links to associated bugs, if any, are in the description.

[coveralls]

Coverage increased (+1.08%) to 86.281% when pulling 82590b0 on akharit-write-buffer into 339b176 on dev.