fix(node-client-sdk): adding docs to clarify FDv2 datasystem will ignore initialConnectionMode

[joker23]

This PR will add clarification to the behavior when datasystems (FDv2) AND is set along with initialConnectionMode is set to offline. In this case, FDv2 datasystems will win out and the initialConnectionMode will be ignore. This behavior is consistent with flutter client sdk.

The additional thing I added here is a warning log for when these configurations are set together so users will know what to expect

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Note

Low Risk
Diagnostic logging and documentation only; connection mode behavior on the FDv2 path is unchanged aside from making misconfiguration visible.

Overview
Clarifies that initialConnectionMode is an FDv1-only option: when a real dataSystem object is configured, FDv2 owns startup connection mode and the top-level option has no effect (aligned with other client SDKs).

validateOptions now logs a warning if both dataSystem and an explicit initialConnectionMode are set, and points callers to dataSystem.automaticModeSwitching.initialConnectionMode with type: 'manual'. Warnings are skipped for null/invalid dataSystem, null initialConnectionMode, or when only one of the two is provided.

NodeOptions JSDoc documents the same precedence. Tests cover option validation edge cases and that createClient still resolves FDv2 mode (e.g. streaming) while emitting the warning when both options are set.

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[joker23]

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