fix: keep unchanged nodes and connections on address-book refresh

[Dosik13]

Description:

Fix the address-book refresh needlessly closing and recreating every consensus node's gRPC connection, even when the fetched address book is unchanged. The churn let in-flight requests race a connection close and fail pre-send with a non-retryable Canceled ("the client connection is closing").

• Match existing nodes against the incoming address book by address and confirm the key, so an unchanged refresh keeps the current nodes
• Skip re-adding nodes already present so their open connections are preserved and only removed or re-addressed nodes are closed
• Add unit tests covering node and connection reuse across an unchanged refresh, using real consensus nodes since the managed-network mocks set key == address

Related issue(s):

Fixes #1762

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
sdk/managed_network.go	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[gsstoykov]

LGTM