Capture `StdoutInterceptor`

[roxblnfk]

Need a global interceptor that buffers test output (stdout).

The interceptor should:

• Wrap test execution with ob_start() / ob_get_clean()
• Store captured output in TestResult metadata
• Renderers decide how to display it (e.g., TeamCity shows always, CLI shows only on failure)
• Track ob_get_level() before and after test. If level changed and test passed — mark as risky (default behavior)

Attribute

#[BufferOutput(enabled: bool)] — controls buffer capture for specific test.

Can be used to:

• Disable capture when globally enabled
• Enable capture when globally disabled

Open questions

how to configure behavior on buffer level mismatch?

Options:

• onLevelMismatch: Status::Failed — single param for any change
• onLevelIncrease / onLevelDecrease — separate params (increase = buffer leak, decrease = test closed external buffer)
• null to ignore

Needs more thought on real use cases.