checkVersionCoherence

One-time pre-flight: confirm the node's ledger is coherent with the client's bundled version, so a skew surfaces as a named warning rather than an opaque Custom error: N mid-submit (#16).

Memoized via VersionCoherenceChecker — the RPC + native read run at most once per SDK instance. NON-BLOCKING by policy (VersionCoherence.HARD_FAIL_ON_SKEW): a skew logs loudly and returns VersionCoherence.Result.Warning, it does NOT throw; a check that can't run returns VersionCoherence.Result.Unknown. Callers may invoke this explicitly to surface the typed result to the UI; the SDK also fires it once before each value-bearing submit.