feat: add `tx::builder` module and initial classic commands #1097

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 57s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	15m 38s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	11m 24s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	15m 38s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	15m 30s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	15m 24s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	15m 39s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	11m 17s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	15m 41s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	15m 30s
	2h 26m 38s

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