fix(postgres): make BasicWaitStrategies safe with container reuse

[malikov73]

What does this PR do?

Makes postgres.BasicWaitStrategies() safe to use with container reuse. The log-based wait (ForLog("database system is ready to accept connections").WithOccurrence(2)) stays as the first gate, and a live-state probe is added after it:

wait.ForExec([]string{"sh", "-c", `command -v pg_isready >/dev/null 2>&1 || exit 0; pg_isready || pg_isready -h 127.0.0.1 -p "${PGPORT:-5432}"`})

The probe prefers the unix socket, falls back to TCP on loopback honoring PGPORT, needs no valid credentials (pg_isready uses PQping, which does not authenticate — custom user/database/password keep working), and is skipped gracefully on images that do not ship pg_isready, preserving the previous behavior for them. On fresh starts the log gate passes only once the server is up, so the probe usually succeeds on its first attempt and adds no meaningful overhead.

It also adds a regression test that puts a reused container through unclean restarts: WithReuseByName, then Stop with a zero timeout while a client session keeps postgres from completing its shutdown checkpoint, so the next start is guaranteed to run crash recovery. The test asserts that a single, retry-free connection attempt succeeds right after Run returns, and that every cycle actually went through crash recovery, so the reproducer cannot degrade silently.

Why is it important?

Container logs survive restarts. On a reused container the readiness lines of the previous run already satisfy the two-occurrence log wait, so Run can return while the current postgres process is still in crash recovery, and clients fail with FATAL: the database system is not yet accepting connections. On main the added test fails consistently with exactly that error.

Related issues

• Closes [Bug]: BasicWaitStrategies() gives false-positive ready signal on reused containers #3671
• Relates docs(postgres): recommend ForSQL strategy #2208

How to test this PR

cd modules/postgres
go test -race -count=1 -run TestBasicWaitStrategies_reusedContainer .

On main the test fails with "the database system is not yet accepting connections"; with this change it passes. The full module suite passes with -race, and make lint is clean.

Follow-ups

• Log-based waits remain reuse-unsafe in general (any module, any wait.ForLog user). A lifecycle-aware log wait (reading logs only since the current StartedAt) would fix the whole class, but occurrence counting needs rethinking there: a restarted data dir logs readiness only once, so WithOccurrence(2) would hang. This PR is intentionally scoped to the postgres module; I can follow up on the general mechanism if there is interest.
• While testing I noticed DockerContainer.Exec never closes the ExecAttach hijacked response, so polling exec strategies leak one daemon connection per poll; I will file that separately.

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