fix(mongodb): SRV ReadPreference decoupling & config robustness

[siiddhantt]

Description

Fixes #682 - MongoDB SRV ReadPreference bug

This PR decouples the read_preference logic from the replica_set field in the MongoDB driver config. Previously, read_preference was only set if replica_set was non-empty, which broke SRV/Atlas connections and caused silent misconfigurations. Now, read_preference is always respected if provided, regardless of replica_set or srv mode. Also fixes hyphenated JSON keys in docs/tests, and clarifies SRV/replica set usage in documentation.

Type of change

• 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?

• Unit tests: Added table-driven tests for all URI scenarios in config_test.go
• Integration: Ran end-to-end proof script with real MongoDB replica set and SRV cluster, verified all edge/breaking cases
• Manual: Confirmed correct URI construction and sync for both SRV and replica set configs

Screenshots or Recordings

• See attached proof video and script output

Documentation

• N/A (bug fix, refactor, or test changes only)

Related PR's (If Any):

• N/A

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Checklist:

• Minimal, focused diff (no unrelated changes)
• All edge/breaking cases verified
• Automated proof attached
• Reviewer feedback from past PRs incorporated