Fix snapshot reference resolution order

[linglingye001]

Fix #180

[Copilot]

Pull request overview

This PR adjusts snapshot reference handling in the configuration settings loader so snapshot-referenced settings are resolved and processed inline, preserving their intended position in the overall selector/setting precedence order.

Changes:

• Replace deferred snapshot reference collection + post-processing with inline snapshot resolution inside processSettings.
• Introduce allowSnapshotRef to prevent nested snapshot reference resolution and snapshotClient to lazily initialize/reuse an App Configuration client for snapshot reads.
• Remove the now-unneeded resolveSnapshotReferences helper and update in-code documentation to reflect the new behavior.

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[zhenlan]

• Introduce allowSnapshotRef to prevent nested snapshot reference resolution and snapshotClient to lazily initialize/reuse an App Configuration client for snapshot reads.

@linglingye001 does it mean a user can disable snapshot reference resolution? Do we support the similar switch in other providers?

[linglingye001]

• Introduce allowSnapshotRef to prevent nested snapshot reference resolution and snapshotClient to lazily initialize/reuse an App Configuration client for snapshot reads.

@linglingye001 does it mean a user can disable snapshot reference resolution? Do we support the similar switch in other providers?

No, allowSnapshotRef is an internal variable. The k8s provider parses the snapshot references in processSettings, fetches the snapshot's settings, allowSnapshotRef false inside a nested snapshot's settings to prevent recursive resolution.