[StatsFetch] Ignore bad decodes

[cristianfr]

Summary

We store the schema in the KVStore, however it's possible for the KVStore to still contain values that are outdated.
To prevent completely failing the fetch, it's better to just provide nulls when the value schema cannot decode a specific value.

Why / Goal

Reliability.

Test Plan

• Added Unit Tests
• Covered by existing CI
• Integration tested (pushed a snapshot version and did a fetch that was failing)

 }, {
    "millis" : 1706486400000,
    "value" : [ 1.65324518E9, 1.65324518E9, 1.65324518E9, 1.65324518E9, 1.65324518E9 ]
  }, {
    "millis" : 1706382000000,
    "value" : null
  }, {
    "millis" : 1706284800000,
    "value" : null
  }, {
    "millis" : 1706270400000,
    "value" : null
  }, {
    "millis" : 1706223600000,
    "value" : null
  }, {

Checklist

• Documentation update

Reviewers