fix(Cluster): pass seconds, not milliseconds, for heartbeat and TCP keepalive

[CodeLieutenant]

Problem

withConnectionHeartbeatInterval() and withTCPKeepalive() converted their argument from seconds to milliseconds. The two cpp-driver functions behind them take seconds:

/* cassandra.h:2530 */
cass_cluster_set_tcp_keepalive(CassCluster*, cass_bool_t enabled, unsigned delay_secs);
/* cassandra.h:2568 */
cass_cluster_set_connection_heartbeat_interval(CassCluster*, unsigned interval_secs);

This is a 1000x error. withConnectionHeartbeatInterval(30.0) sent 30000 seconds, about 8.3 hours, which disabled heartbeats. Dead connections then stayed in the pool until a request failed on them.

The defaults in php_scylladb_cluster_builder_new are raw seconds (connection_heartbeat_interval = 30), so seconds was always the intended unit. Only the setters were wrong.

Changes

• src/Cluster/Builder.c — add php_scylladb_set_interval_seconds() next to the existing millisecond helper. withConnectionHeartbeatInterval uses it.
• src/Cluster/Builder.c — withTCPKeepalive stores ceil(delay) instead of ceil(delay * 1000).
• src/Cluster/BuilderHandlers.c — get_properties no longer divides tcpKeepalive by 1000. That divide was the mirror of the same bug, so the property read back the value the user passed in and hid the defect.

The three genuine millisecond settings are untouched: withConnectTimeout, withRequestTimeout, and withReconnectInterval.

Public API

No change. Both methods still take seconds.

Tests

New tests/Unit/Cluster/BuilderTest.php, 13 cases:

• defaults: connectionHeartbeatInterval is 30, tcpKeepalive is null
• seconds round-trip through the exposed connectionHeartbeatInterval and tcpKeepalive properties
• withTCPKeepalive(null) disables keepalive
• negative values throw Cassandra\Exception\InvalidArgumentException
• reconnectInterval as a control, because it stays in milliseconds internally

Full unit suite on PHP 8.5 NTS: 816 passed. One pre-existing failure in tests/Unit/Uuid/UuidTest.php:112, a cross-process child-spawn quirk that is unrelated to this change.

Note for the reviewer

Both methods take float but now truncate to whole seconds through ceil, so 0.5 becomes 1. That matches the C API, which has no sub-second granularity, but the PHP signature still advertises precision it cannot deliver. Changing the stub to int is a BC break and belongs in a separate decision.

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