Fix DockerDesktopClientProviderStrategy always being applicable

[seonwooj0810]

Fixes #11829

Problem

DockerDesktopClientProviderStrategy.isApplicable() returns true on Linux/macOS even when Docker Desktop is not installed, after which getTransportConfig() throws a NullPointerException.

The cause is a Lombok pitfall. The socketPath field is declared with @Getter(lazy = true):

@Getter(lazy = true)
@Nullable
private final Path socketPath = resolveSocketPath();

Lombok rewrites a lazy field into an AtomicReference that holds the memoized value, so the field itself is never null. isApplicable() checked the raw field rather than the generated accessor:

return (SystemUtils.IS_OS_LINUX || SystemUtils.IS_OS_MAC) && this.socketPath != null; // AtomicReference is never null

As a result the strategy is always considered applicable, and getTransportConfig() then dereferences getSocketPath() (which resolves to null when no ~/.docker/desktop/docker.sock or ~/.docker/run/docker.sock exists), producing the NPE reported in #11829.

Fix

Use the Lombok-generated getSocketPath() accessor — which resolves the lazy value to the actual Path (or null) — instead of reading the backing field directly. getDescription() and getTransportConfig() already use the accessor; this aligns isApplicable() with them.

return (SystemUtils.IS_OS_LINUX || SystemUtils.IS_OS_MAC) && getSocketPath() != null;

Tests

Added DockerDesktopClientProviderStrategyTest (no Docker required) covering both directions by pointing user.home at a temp directory:

• notApplicableWhenDockerDesktopSocketIsMissing — no Docker Desktop socket present ⇒ isApplicable() is false. This fails on the current code (returns true) and passes with the fix.
• applicableWhenDockerDesktopSocketExists — a .docker/desktop/docker.sock present ⇒ isApplicable() is true.

Verification done: ran ./gradlew :testcontainers:test --tests "org.testcontainers.dockerclient.DockerDesktopClientProviderStrategyTest" — both tests pass with the fix; reverting the one-line change makes notApplicableWhenDockerDesktopSocketIsMissing fail, confirming the test reproduces the bug. ./gradlew spotlessApply reports no formatting changes.