txBroadcast: Stabilize to version 1 (#4169)
This PR stabilizes the txBroadcast API to version 1.
Ideally needs:
- https://github.com/paritytech/polkadot-sdk/pull/4050
- https://github.com/paritytech/polkadot-sdk/pull/3772
cc @paritytech/subxt-team
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Signed-off-by: Alexandru Vasile <[email protected]>