fix: Update DataSystemConfig to accept list of synchronizers

[keelerm84]

Note

Medium Risk
Changes core data-synchronization failover logic (including FDv1 fallback) and alters config shape/API, which can affect initialization and runtime update behavior across environments.

Overview
Updates the experimental data system configuration to use an ordered list of synchronizers rather than primary_synchronizer/secondary_synchronizer, and updates the builder API (ConfigBuilder.synchronizers(*builders)) to require at least one synchronizer.

Refactors the FDv2 runtime to iterate through any number of synchronizers with generalized fallback/recovery behavior (including permanent removal on failure and optional switch to the FDv1 fallback synchronizer), and updates contract-test parsing plus unit tests to match the new list-based configuration.

CI contract tests are bumped to v3.0.0-alpha.3 and YAML quoting is normalized for boolean-like inputs.

^{Written by Cursor Bugbot for commit 697b0c2. This will update automatically on new commits. Configure here.}

[jsonbailey]

I added a suggestion but don't consider it a blocker.

[jsonbailey]

In Ruby I ended up collapsing this down to a single result, essentially adding the remove sync and fallback as options of the Conditional Directive. From my understanding they are all independent of each other. If you have fallback, you don't care about the other two, if you have remove sync, you don't care about the conditional directive, so there isn't a need to have all three returned.