fix: render ClickHouse timestamp interval bounds

[karakanb]

What

Fix ClickHouse time_interval timestamp deletes by rendering parseable DateTime64 bounds.

Changes

• Use space-separated microsecond timestamps inside explicit toDateTime64 expressions.
• Cover the first incremental run and an exact rerun end to end.

How to test

1. Run make format and make test.
2. Run the ClickHouse integration suite in integration-tests/cloud-integration-tests/clickhouse.

Risk & rollback

• Risk: Low; the change only affects ClickHouse timestamp-granularity interval bounds.
• Rollback: Revert the merge commit.

Checklist

• Unit tests added or updated (make test)
• Builds and lint pass (make build-no-duckdb, make format)
• Integration tests pass if affected (make integration-test)
• No unrelated changes included
• Tested locally

Security

• No secrets, credentials, or PII in this change
• No new dependencies with known vulnerabilities
• Security implications considered (if applicable)

Related issues

Closes #2419