fix: exclude non-string findAndRerank passages

[erichare]

What this PR does:

findAndRerank sends numbers and booleans in the rerankOn field to the reranker as text, e.g. 42 becomes "42" and 1.50 becomes "1.5". Objects and arrays fail the whole request with UNEXPECTED_SERVER_ERROR.

Only string values are now used as passages. Other types are excluded, the same as missing, null, and blank values, matching the docs.

Updates the ScoredDocument passage cases and adds an integration test that checks only the string passage reaches the reranker. The 44 reranking unit tests and FindAndRerankCollectionSuccessIntegrationTest pass on Java 21 against DSE.

Which issue(s) this PR fixes:
Fixes #2613
Fixes #2611

Checklist

• Changes manually tested
• Automated Tests added/updated
• Documentation added/updated
• CLA Signed: DataStax CLA

[github-actions]

📉 Unit Test Coverage Delta vs Main Branch

Metric	Value
Main Branch	54.71%
This PR	54.70%
Delta	🔴 -0.02%
⚠️ Coverage decreased

[github-actions]

Unit Test Coverage Report

Overall Project	54.7%	🍏
Files changed	100%	🍏

File	Coverage
ScoredDocument.java	92.04%	🍏

[erichare]

@Hazel-Datastax this conflicts with the non-string rerankOn cases #2638 pins. I followed the docs (exclude them), but holding as draft until we agree which way to go.

[github-actions]

📈 Integration Test Coverage Delta vs Main Branch (dse69-it)

Metric	Value
Main Branch	72.95%
This PR	72.96%
Delta	🟢 +0.01%
✅ Coverage improved!

[github-actions]

Integration Test Coverage Report (dse69-it)

Overall Project	72.96%	🍏
Files changed	100%	🍏

File	Coverage
ScoredDocument.java	56.75%	🍏

[github-actions]

📈 Integration Test Coverage Delta vs Main Branch (hcd-it)

Metric	Value
Main Branch	74.27%
This PR	74.29%
Delta	🟢 +0.01%
✅ Coverage improved!

[github-actions]

Integration Test Coverage Report (hcd-it)

Overall Project	74.29%	🍏
Files changed	100%	🍏

File	Coverage
ScoredDocument.java	59.17%	🍏