Merge consecutive spin-loop blocks and remove redundant thread switches

[eupp]

The trace can contain several consecutive thread switches to the blocks of the same spin-loop.

Example:

|         /* The following events repeat infinitely: */                                |
|     ┌╶> state ➜ 0 at FutureTask.awaitDone(FutureTask.java:406)                       |
|     |   LockSupport.park(FutureTask#1) at FutureTask.awaitDone(FutureTask.java:447)  |
|     └╶╶ switch (reason: active lock detected)                                        |
|                                                                                      |
|                                                                                      |
|                                                                                      |
|                                                                                      |
|         /* The following events repeat infinitely: */                                |
|     ┌╶> state ➜ 0 at FutureTask.awaitDone(FutureTask.java:406)                       |
|     |   LockSupport.park(FutureTask#1) at FutureTask.awaitDone(FutureTask.java:447)  |
|     └╶╶ switch (reason: active lock detected)                                        |

lincheck/src/jvm/test/resources/expected_logs/run_concurrent_test/thread_pool/thread_pool_jdk17.txt

Line 106 in f0b6b22

| └╶╶ switch (reason: active lock detected) | | |

We need to fix this by merge several consecutive spin-loop blocks, and do not show redundant thread switches.