soroban-rpc: preflight: Exclude temporary expired entries from SnapshotSource #2581

Job	Run time
Integration tests (ubuntu-20.04, 1.20.1)	27m 55s
Build (ubuntu-latest, x86_64-unknown-linux-gnu, amd64)	3m 33s
Unit tests (ubuntu-20.04, 1.20.1)	4m 16s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, arm64)	4m 33s
Build (macos-latest, x86_64-apple-darwin, amd64)	6m 45s
Build (macos-latest, aarch64-apple-darwin, arm64)	5m 45s
Build (windows-latest, x86_64-pc-windows-gnu, amd64)	11m 27s
	1h 4m 14s

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