Update flagd-testbed to v3.6.2 and fix in-process evaluation edge cases

[toddbaert]

Summary

Update the flagd-testbed dependency to v3.6.2 and fix the in-process evaluation to pass all new edge-case tests.

Testbed v3.6.2 adds coverage for the edge cases identified in:

• [BUG] sem_ver operator parsing behavior differs across SDK implementations flagd#1873 (sem_ver parsing inconsistencies)
• [BUG] Custom operator error return values are inconsistent across SDK implementations flagd#1874 (custom operator error return values)
• [BUG] $evaluators/$ref resolution: no parse-time validation, non-deterministic ordering, and missing Rust support flagd#1875 ($evaluators/$ref resolution gaps)

Bugs to fix

sem_ver (open-feature/flagd#1873)

1. sem_ver accepts partial versions ("1.2", "1") by coercing missing components to 0; should reject partial versions to match the standardized behavior (strict X.Y.Z required)

Custom operator error returns (open-feature/flagd#1874)

2. fractional throws JsonLogicEvaluationException on no-bucket-match; should return null to trigger default variant fallback instead of propagating an exception

$evaluators/$ref resolution (open-feature/flagd#1875)

3. No diagnostic feedback on unresolved $refs at parse time; failure only surfaces at evaluation time via JsonLogicEvaluationException
4. Non-deterministic $evaluators replacement ordering (HashMap iteration); should use deterministic iteration

Parent: open-feature/flagd#1904