calculate keepalive timeout dynamically with formula

[marregui]

card: https://hivemq.kanbanize.com/ctrl_board/57/cards/38362/details/

• Removed hardcoded KEEP_ALIVE_TIMEOUT_MS = 30_000
• Added a new public method getKeepAliveTimeoutMs() that computes the timeout dynamically using the formula:
  keepAliveIntervalMs × (keepAliveFailuresAllowed + 1) + 5000ms (safety margin)
• Updated isKeepAliveHealthy() to use the dynamically computed timeout

Formula Explanation

With default ConnectionOptions:

• keepAliveIntervalMs = 10,000ms (10 seconds)
• keepAliveFailuresAllowed = 3
• Safety margin = 5,000ms

Result: 10,000 × (3 + 1) + 5,000 = 45,000ms (45 seconds)

This is more appropriate than the previous hardcoded 30 seconds because:

• The OPC UA client allows 3 failures before considering the connection dead
• With a 10-second keep-alive interval, worst case is 30 seconds before failure detection
• The extra interval + safety margin prevents false positives

[caoccao]

LGTM

[caoccao]

Could we give a name to that magic number?