`ClassNotFoundException` for `SentryReactorUtils` when excluding the `sentry-reactor` dependency

### Integration

sentry

### Java Version

17

### Version

8.23.0

### Steps to Reproduce

Use `spring-boot-jakarta` dependency but exclude `sentry-reactor` dependency in WebFlux sample. Have a `@GetMapping` method that throws an exception.

### Expected Result

Exception captured to Sentry

We could have a `SentryWebExceptionHandlerWithThreadLocalAccessor` in addition to `SentryWebExceptionHandler`, then have `SentryWebExceptionHandler` not use `SentryReactor`. This would mimic what we do for `SentryWebFilterWithThreadLocalAccessor` and `SentryWebFilter`.

### Actual Result

`Caused by: java.lang.ClassNotFoundException: io.sentry.reactor.SentryReactorUtils`

and

`reactor.netty.http.client.PrematureCloseException: Connection prematurely closed BEFORE response`

and the `ClassNotFoundException` is reported to Sentry instead of the real exception.

從 spring-boot-jakarta WebFlux 範例開始，在排除 sentry-reactor 後重現此故障。比較 SentryWebExceptionHandler、SentryWebFilter 與 SentryWebFilterWithThreadLocalAccessor；完成的標準是擷取到真正的 exception，且不會出現 SentryReactorUtils ClassNotFoundException。

由索引模型根據 Issue 內容生成。