refactor(bthread): make TaskControl metric ownership explicit

[darion-yaphet]

What problem does this PR solve?

Problem Summary:

TaskControl stored per-tag bvar metrics as raw pointers. In addition, each cumulative-time PassiveStatus received a heap-allocated callback argument with no explicit owner. Since PassiveStatus does not own that argument, its lifetime was unclear and could leak when TaskControl is destroyed.

What is changed and the side effects?

Changed:

• Replace the four per-tag bvar raw-pointer vectors with std::unique_ptr containers.
• Add explicit ownership for each CumulatedWithTagArgs callback argument.
• Preserve metric names, access patterns, and scheduler behavior.
• Keep callback arguments alive until their corresponding PassiveStatus is destroyed.

Side effects:

• Performance effects: No steady-state impact expected. Ownership changes occur only during TaskControl initialization/destruction.
• Breaking backward compatibility: None; no public API or metric name changes.

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Check List:

• The modified task_control.cpp CMake object target compiles successfully.
• git diff --check passes.
• Full bthread test suite was not run because the current build is blocked by an unrelated brpc::EPROGREADTIMEOUT compilation error.
• No new feature; no additional behavior test required.