Fix Prometheus Counter anti-pattern: remove _value access

[Copilot]

Prometheus Counters were being incorrectly accessed via internal _value attribute to calculate deltas. This violates Prometheus design principles where counters should only be incremented.

Changes

• Added tracking dictionaries to store last exported values for request, cost, and savings counters
• Calculate deltas from tracked state instead of accessing Counter._value
• Ensure counters are only incremented via .inc(), never set

Before

counter = self.request_total.labels(primitive_name=name, status="success")
current_value = getattr(counter, '_value', None)
if current_value is not None:
    increment = throughput_metrics.total_requests - current_value.get()
    if increment > 0:
        counter.inc(increment)

After

counter = self.request_total.labels(primitive_name=name, status="success")
last_value = self._last_request_totals.get(labels_success, 0.0)
increment = throughput_metrics.total_requests - last_value
if increment > 0:
    counter.inc(increment)
    self._last_request_totals[labels_success] = throughput_metrics.total_requests

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[theinterneti]

This PR is relevant to the framework-first strategy but has significant merge conflicts that require manual resolution.

[Copilot]

Copilot wasn't able to review any files in this pull request.

[theinterneti]

✅ Merge conflicts resolved

Merged feature/keploy-framework into this branch and resolved conflicts in prometheus_exporter.py.

Resolution Strategy:

• Accepted the incoming implementation from feature/keploy-framework
• Uses cleaner variable naming (_last_request_total vs _last_request_totals)
• More explicit temporary variables (current_total, last_total) for better readability

The PR is now ready for review and should be mergeable.