[intervalprocessor] Add delta temporality metrics support

[SumitDalavi]

Description

Currently, intervalprocessor ignores delta temporality metrics and simply passes them through. This PR adds support for accumulating delta metric values across the interval using a local copy of the deltatocumulativeprocessor's data addition utilities.

To maintain the "smallest maintainable change" principle and avoid breaking the existing deltatocumulativeprocessor, the data-addition logic was localized into intervalprocessor. (We can extract this into a shared internal/exp/metrics/data package in a future PR if desired).

Link to tracking issue

Fixes #50845

Testing

• Updated existing intervalprocessor tests to assert that delta metrics are properly aggregated over intervals.
• Verified all targeted component tests in processor/intervalprocessor/... pass cleanly.

Documentation

• N/A

Authorship

• I, a human, wrote this pull request description myself.

[SumitDalavi]

Hi! I've opened this PR to add delta temporality metrics support for the \intervalprocessor. To keep this as a minimal and safe change (without risking regressions in the existing \deltatocumulativeprocessor), I duplicated the data-addition logic into \intervalprocessor/internal/data.

However, as a future improvement or if reviewers prefer doing it in this PR, I propose we extract these data-addition utilities into a shared internal package (e.g., \internal/exp/metrics/data).

Looking forward to your feedback!