fix: validate addresses in alw miner post before committing to chain

[wdeveloper16]

Closes: #155

Summary

alw miner post accepted any string as a BTC or TAO address and committed it to the subnet without validation. A miner who typos their receiving address becomes unable to receive funds from matched swaps — their collateral is at risk and users matched to them will experience failed fulfillments.

What changed

allways/cli/swap_commands/pair.py

• After chains and addresses are resolved (but before showing the confirmation summary), creates chain providers with check=False and calls is_valid_address() for both the source and destination address
• Both BitcoinProvider and SubtensorProvider validate locally — no network connections are made
• Rejects with a clear [red]Invalid <ChainName> address: <addr>[/red] message and returns early

tests/test_pair_validation.py (new, 4 tests)

• Invalid src address rejected
• Invalid dst address rejected
• Valid addresses proceed to confirmation
• Both invalid shows only the first error

Test Case

Before:

After:

[anderdc]

duplicate identified

[wdeveloper16]

Hi, @anderdc
Would you please clarify the closing reason more?

[wdeveloper16]

I think it's really needed before moving fulfillment

[wdeveloper16]

Hi, @anderdc
Could you review the PR, please?
My logic is smart and clear than #133.