Add doc comments for `L1HandlerTx` #6450

Job	Run time
ensure-windows	11m 24s
ensure-wasm	1m 40s
cairofmt	6s
dojo-core-test	4m 57s
test	12m 31s
clippy	4m 53s
dojo-spawn-and-move-example-test	5m 11s
dojo-world-bindings-check	2m 44s
fmt	1m 20s
docs	2m 18s
test-hurl	1m 32s
	48m 36s

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