[deltatocumulativeprocessor] Introduce an upper bound for exp histogram buckets

[euroelessar]

Description

This PR introduces a limit on the maximum number of exponential histogram buckets within the deltatocumulativeprocessor. Previously, when merging delta metrics into cumulative metrics, the resulting exponential histograms could grow very large, potentially causing excessive memory usage and processing overhead. By capping the number of buckets at 160 and dynamically downscaling histograms when necessary, this change ensures that the processor remains efficient and stable even when handling large, merged exponential histograms.

Link to tracking issue

Fixes #33277

Testing

Added unit tests for edge cases.

Documentation

Updated changelog.

[euroelessar]

@sh0rez Please have a look, it's an alternative take on #34157, it avoids any extra memory allocations and could be easier to follow.
All changes are in ExpHistogram.Add (and Merge called from it), as it's the only place which can grow the histogram.