[Data] Concurrency Cap Backpressure tuning (#58163)

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## Description
> Briefly describe what this PR accomplishes and why it's needed.


### [Data] Concurrency Cap Backpressure tuning
- Maintain asymmetric EWMA of total queued bytes (this op + downstream)
as the typical level: level.
- Maintain asymmetric EWMA of absolute residual vs the previous level as
a scale proxy: dev = EWMA(|q - level_prev|).
- Define deadband: [lower, upper] = [level - K_DEVdev, level +
K_DEVdev].
If q > upper -> target cap = running - BACKOFF_FACTOR (back off)
If q < lower -> target cap = running + RAMPUP_FACTOR (ramp up)
Else -> target cap = running (hold)
- Clamp to [1, configured_cap], admit iff running < target cap.

## Related issues
> Link related issues: "Fixes #1234", "Closes #1234", or "Related to
#1234".

## Additional information
> Optional: Add implementation details, API changes, usage examples,
screenshots, etc.

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Signed-off-by: Srinath Krishnamachari <[email protected]>
Signed-off-by: Srinath Krishnamachari <[email protected]>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: srinathk10