feat: add tx sign/send and Stellar trait #770

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 45s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 19s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	11m 57s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	19m 11s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	23m 20s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 35s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 12s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	10m 48s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	24m 4s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 9s
	2h 51m 20s

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