docs: add build, test, and Soroban-CLI deployment guide

[Jagadeeshftw]

Summary

Adds docs/escrow/build-deploy.md, an end-to-end guide covering:

• Running the workspace test suite (cargo fmt --all -- --check, cargo build, cargo test).
• Building the release WASM (cargo build --release --target wasm32-unknown-unknown), with the real [profile.release] values quoted from Cargo.toml (opt-level = "z", lto = true, panic = "abort", plus overflow-checks, codegen-units = 1, strip).
• Where the artifact lands: target/wasm32-unknown-unknown/release/escrow.wasm (shared workspace target/).
• Deploying to testnet with the Stellar/Soroban CLI, with version-sensitive flags marked ⚠️.
• Invoking init(admin) on the deployed contract id.
• A post-deploy sanity check calling version() and get_schema_version().

Notes the workspace members = ["contracts/escrow"]. Links the guide from README.md. No code changed.

Closes #45

Test output (gate, unchanged code)

test result: ok. 23 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.17s

Security notes: Docs-only change; no contract code, dependencies, or build profile are modified.

[mikewheeleer]

clean build/test/deploy guide, thanks. merging 👍