soroban-rpc: Use External Soroban Crates #13

Job	Run time
Build (ubuntu-latest, x86_64-unknown-linux-gnu, amd64)	2m 29s
Integration tests (ubuntu-20.04, 1.21, .CLI.)	14m 51s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, arm64)	3m 1s
Integration tests (ubuntu-20.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	15m 25s
Unit tests (ubuntu-20.04, 1.21)	5m 53s
Build (macos-latest, x86_64-apple-darwin, amd64)	3m 51s
Integration tests (ubuntu-22.04, 1.21, .CLI.)	15m 3s
Unit tests (ubuntu-22.04, 1.21)	6m 16s
Build (macos-latest, aarch64-apple-darwin, arm64)	5m 12s
Integration tests (ubuntu-22.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	14m 49s
Build (windows-latest, x86_64-pc-windows-gnu, amd64)	8m 45s
	1h 35m 35s

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