Bloom checksum work

[paul1r]

What this PR does / why we need it:

Previously, MergeBuilder.Build() used a checksum of the bloom page headers. This PR does multiple things in relation to checksums, including:

• Augmenting the bloom page header to have a checksum of the data of the bloom page (in order to capture the actual content of the blooms). As a result, a bloom page with a single bloom should now differ from another bloom page with a single bloom, unless the contents of the two blooms are exactly equal.
• Add checksum calculations for the block options
• Return the checksums when Close()ing the series data
• Augmenting the checksum calculations to include the checksum of the bloom pages, the series pages, and the block options

This will render existing bloom data invalid.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
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