Test: Enable fuzz tests for native histograms

[harry671003]

Changes

This PR mainly enables native histogram fuzz tests. It also addresses some of the issue identified while testing.

In addition it makes the following changes:

• Excluding duplicate label set errors from test comparison
  • Duplicate label check in Thanos engine doesn't always work similar to Prometheus engine.
• Removing known optimizations from sample stats checks
  • Thanos engine will output less samples
• Fixing the buckets for NH load to avoid zero buckets.
  • Histogram.Equals() doesn't equate histograms with zero values.
• Compare histograms approximately.
• Allow fractional errors while comparing floats

Excluding known edge cases

Excluding some known edge cases from native histgram fuzz tests such as:

• sort() and other family functions. Thanos engine doesn't filter out NH samples. Prometheus does.
• predict_linear with step invariant - Thanos engine is unable to handle this case today.
• timestamp() - Fix in Implement timestamp() for native histograms #598

Race condition in Prometheus engine

• https://github.com/thanos-io/promql-engine/actions/runs/16230914496/job/45833407585
• There appears to be some race condition in old engine when the storage is shared across multiple runs.
• This causes the Prometheus engine to not return the buckets.
• This is not reproducible outside the fuzz tests and unable to find the root cause.

        enginefuzz_test.go:341: case 31 error mismatch.
            new result: {pod="nginx-1"} =>
            {count:66, sum:0, (0.5,1]:1, (1,2]:2, (2,4]:63} @[0]
            {count:66, sum:0, (0.5,1]:1, (1,2]:2, (2,4]:63} @[4000]
            
        old result: {pod="nginx-1"} =>
            {count:66, sum:0} @[0]
            {count:66, sum:0} @[4000]
            {count:66, sum:0} @[8000]    

Fix: prometheus/prometheus#16879

[harry671003]

Waiting for #609

[yeya24]

Thanks. This is great work.
I have some small questions and nothing blocks this PR

[yeya24]

Let's enable the fuzz tests and see how it goes. We can always adjust things if needed