feat: add tx sign/send and Stellar trait #541

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 29s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 6s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	11m 43s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	15m 1s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 21s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 16s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 33s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	17m 10s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	18m 15s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 56s
	2h 44m 50s

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