Support custom ParkingLot number

[chenBright]

What problem does this PR solve?

Issue Number: #2849 (comment)

Problem Summary:

What is changed and the side effects?

Changed:

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull Request Overview

This PR adds support for configurable parking lot numbers per tag in the bthread system, replacing the hardcoded PARKING_LOT_NUM constant with a runtime configurable value. The changes enable users to customize the number of parking lots per tag through a new flag.

• Removes hardcoded PARKING_LOT_NUM = 4 constant and replaces it with configurable _pl_num_of_each_tag
• Adds new command-line flag bthread_parking_lot_of_each_tag to control parking lot count
• Updates parking lot iteration logic to use the configurable value instead of hardcoded constant

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/bthread/task_control.h	Removes hardcoded PARKING_LOT_NUM constant, renames member variable to _tagged_pl, and adds _pl_num_of_each_tag field
src/bthread/task_control.cpp	Implements configurable parking lot logic using new flag and updates iteration patterns
src/bthread/bthread.cpp	Defines new bthread_parking_lot_of_each_tag flag and contains unrelated namespace cleanup

[wwbmmm]

LGTM

[yanglimingcn]

一般parkinglot的数量和worker的数量，怎么样是比较合适的。

[yanglimingcn]

LGTM

[chenBright]

一般parkinglot的数量和worker的数量，怎么样是比较合适的。

可以调整为平均4/8个worker线程共享一个ParkingLot，在实际场景测试一下效果才能确定个数。

我们的场景是worker线程数多（200+）、大量轻量bthread，火焰图显示在ParkingLot futex内核自旋锁的操作消耗了过多的CPU。