Fixes an issue with AppendableMemory that can cause MSQ jobs to fail

[LakshSingla]

Description

This PR fixes a bug with the AppendableMemory where it fails the allocation even though there is enough space to complete it.

There are 2 components to the allocation -

1. availableToReserve which returns the max allocation that can be requested. It returns the max of the available memory in the allocator and the free space in the last allocated block
2. reserveAdditional makes the allocation and reserves the data

(2) fails if the additionally reserved memory can be satisfied with the last allocated block but not by the allocator. Check the added test case for a better description of how this bug can arise.

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Key changed/added classes in this PR

• MyFoo
• OurBar
• TheirBaz

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This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.