feat: Add FDv2 data system support to NodeClient

[joker23]

SDK-2468

---

Note

Medium Risk
Touches core flag data path and connection/offline/event-sending behavior when FDv2 is enabled; FDv1 path is largely preserved but shared connection-mode APIs changed implementation.

Overview
Adds FDv2 to the Node client when dataSystem is set: the data manager factory wires createFDv2DataManagerBase (desktop defaults/transition table) instead of NodeDataManager, with buildQueryParams for client-side ID (auth / h) and empty params plus hash warnings in mobile key mode.

Connection mode is tracked on NodeClient for both FDv1 and FDv2. FDv2 setConnectionMode validates modes, no-ops after close or when unchanged, serializes concurrent transitions (flush before offline, then event sending + data manager), and keeps the queue usable after a failed flush. getConnectionMode / isOffline read the cached mode rather than the FDv1 data manager.

CI runs FDv2 contract tests (harness v3.1.1-alpha.6) against the same long-lived test service (stop_service: 'false' on FDv1), with an FDv2 suppression list including one new skipped wrapper test. Unit coverage lives in NodeClientFDv2.test.ts.

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[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
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Uncompressed size: 129044 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
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Uncompressed size: 114243 bytes

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@launchdarkly/browser size report
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[joker23]

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[joker23]

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