[Internal] Thin Client Integration: Fixes Exclude regions check for thinclient mode.

[aavasthy]

Pull Request Template

Description

This change resolves an issue where per-request region exclusions were not honored when the SDK operated in thin client mode. Previously, requests configured with ExcludeRegions would still route to theprimary thin client endpoint regardless of the customer's regional preferences, preventing them from steering traffic away from specific regions during operational events. With this fix, thin client requestrouting now filters available endpoints against the excluded region list in a manner consistent with the standard gateway path, restoring expected behavior for both individual operations and cross-region hedging scenarios. The change is scoped narrowly to the thin client resolution path, preserves all existing routing semantics when no exclusions are specified, and is covered by new unit and integration test.

Type of change

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• Bug fix (non-breaking change which fixes an issue)

Closing issues

To automatically close an issue: closes #5789

Changelog

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[kushagraThapar]

Thanks @aavasthy, overall looks good, it would be good to have some more testing on all regions excluded code path and end to end hedging tests?