Flaky test: HttpTransportTests.testAccessTokenAuth / testBearerTokenAuth bind a random fixed port and fail with FatalStartupException

## Description

`HttpTransportTests.testAccessTokenAuth` and `HttpTransportTests.testBearerTokenAuth`
(module `client-v2`) start their WireMock server on a **randomly chosen fixed port**:

```java
int randomPort = ThreadLocalRandom.current().nextInt(3000, 65535);
WireMockServer mockServer = new WireMockServer(WireMockConfiguration
.options().port(randomPort).notifier(new ConsoleNotifier(false)));
mockServer.start();
```

`client-v2/src/test/java/com/clickhouse/client/HttpTransportTests.java:1307` (testBearerTokenAuth)
and `:1385` (testAccessTokenAuth).

If that port is already taken, `mockServer.start()` throws immediately and the test fails.
There is no retry and no fallback. The chosen range (3000-65535) overlaps the Linux
ephemeral port range (`/proc/sys/net/ipv4/ip_local_port_range` = 32768-60999 on the CI
runners), so any outbound socket held by a concurrently running test, by Maven, or by
another job on the same runner can take the port.

Every **other** WireMock server in the same file already uses `.dynamicPort()` (about 20
occurrences, e.g. lines 895, 1465, 1854). Only these two tests use the fixed-port form.

### Steps to reproduce
1. Occupy an arbitrary subset of TCP ports in 3000-65535 on the machine (this simulates a
loaded CI runner). For the numbers below, 29768 ports (3000-32767, 47.6% of the range)
were held by a helper process; the ephemeral range was left free so outbound
connections still worked.
2. Run the test repeatedly:
`mvn -B -pl client-v2 -DskipUTs=true -Dit.test=HttpTransportTests#testAccessTokenAuth -Dfailsafe.failIfNoSpecifiedTests=false -DfailIfNoTests=false verify`
3. The test fails on roughly the fraction of the range that is occupied.

Observed: **4 failures out of 12 runs** (33%, expected ~48%), each with the same signature
as CI but a different port each time:

```
run 1: PASS
run 2: FAIL -> Failed to bind to /0.0.0.0:10117
run 3: FAIL -> Failed to bind to /0.0.0.0:15282
run 4: PASS
run 5: FAIL -> Failed to bind to /0.0.0.0:18977
run 6..9: PASS
run 10: FAIL -> Failed to bind to /0.0.0.0:14457
run 11..12: PASS
```

Contrast: `HttpTransportTests#testSessionSettingsClientAndOperationLevels`, which uses
`.dynamicPort()`, passed **6/6** under exactly the same port contention.

### Error Log or Exception StackTrace

Verbatim from CI (`amazon JDK 17` / "Test all modules",
https://github.com/ClickHouse/clickhouse-java/actions/runs/32807717786/job/97681145686):

```
[ERROR] com.clickhouse.client.HttpTransportTests.testAccessTokenAuth -- Time elapsed: 0.005 s <<< FAILURE!
com.github.tomakehurst.wiremock.common.FatalStartupException: java.io.IOException: Failed to bind to /0.0.0.0:32783
[ERROR] HttpTransportTests.testAccessTokenAuth:1388 » FatalStartup ... Failed to bind to /0.0.0.0:32783
[ERROR] Tests run: 897, Failures: 1, Errors: 0, Skipped: 3
```

Note `32783` is inside the OS ephemeral range. The other 34 legs of the same matrix passed
on the same commit, and the change under test touched only client-v2 metadata handling -
nothing in the auth path - so the failure is not attributable to the code under test.

### Expected Behaviour

The test binds a free port and never fails because of port allocation. The `Client.Builder`
already receives the port from `mockServer.port()` after start, so nothing needs the port
value in advance.

### Code Example

Suggested fix - use the same form as the rest of the file, at both sites:

```java
WireMockServer mockServer = new WireMockServer(WireMockConfiguration
.options().dynamicPort().notifier(new ConsoleNotifier(false)));
mockServer.start();
```

`.dynamicPort()` binds port 0, so the kernel picks a port that is guaranteed free, and
`mockServer.port()` (already used throughout both tests) returns the actual port. The
`randomPort` local becomes unused and can be dropped, together with the now-unneeded
`ThreadLocalRandom` usage if no other test needs it.

Please do not fix this with a retry loop or a narrower random range - both leave the race
in place. There is no product-code race here; the defect is entirely in the test fixture.

### Configuration

#### Environment
* [ ] Cloud
* Client version: `main` @ `667cbe90b`
* Language version: OpenJDK 17.0.18
* OS: Ubuntu 24.04 (container), also seen on the `amazon JDK 17` CI runner

#### ClickHouse Server
* ClickHouse Server version: not relevant - the test uses a mocked WireMock server and
returns early when `isCloud()`.

---

Found by our PR monitor: the failure was seen on unrelated PRs whose changes do not touch
the auth path, and it is already tracked internally as a known non-routing flake. Verified
here by reproducing the bind failure locally under port contention, not by inspection only.