Document transaction module (backport #22440) (#22664)

* Document transaction module (#22440)

* Document transaction module

* example_mocks is only for feature = full

(cherry picked from commit 8dd62854fa)

# Conflicts:
#	sdk/src/transaction/mod.rs

* Fix conflicts

Co-authored-by: Brian Anderson <andersrb@gmail.com>
Co-authored-by: Tyera Eulberg <tyera@solana.com>

sdk/Cargo.toml

@@ -84,6 +84,7 @@ wasm-bindgen = "0.2"
 js-sys = "0.3.55"
 
 [dev-dependencies]
+anyhow = "1.0.45"
 curve25519-dalek = "3.2.0"
 tiny-bip39 = "0.8.2"