fix: resolve Dependabot security vulnerabilities (#89, #90, #87, #21)

[aimansharief]

• Bump org.apache.zookeeper:zookeeper 3.8.4 → 3.8.6 in root dependencyManagement (fixes CVE: hostname verification bypass + improper config handling)

• Migrate graph-engine_2.13 tests from cassandra-unit to testcontainers-cassandra; upgrade snakeyaml 1.33 → 2.0 (fixes SnakeYaml Constructor Deserialization RCE); remove cassandra-unit:3.11.2.0 and its associated netty/snappy/jna overrides; add CassandraTestSupport singleton with reflection-based session injection

• Bump org.apache.poi:poi-ooxml 3.17 → 5.4.0 and xmlbeans 3.0.0 → 5.2.1 in platform-common (fixes improper input validation in OOXML file parsing)

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

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Test Configuration:

• Software versions: Java 11, scala-2.12, play-2.7.2
• Hardware versions: 2 CPU/ 4GB RAM

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
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