Fix BTC segwit regex to accept testnet (tb) addresses

[uttam12331]

Summary

btc_address() rejects every valid testnet bech32/segwit address.

The segwit branch is guarded by:

if value[:2] in ("bc", "tb")

so both mainnet (bc) and testnet (tb) HRPs are routed into the regex — but the regex only accepts bc or tc:

re.compile(r"^(bc|tc)[0-3][02-9ac-hj-np-z]{14,74}$").match(value)

tc is not a valid Bitcoin human-readable part (mainnet is bc, testnet is tb — see BIP173). Because the guard never lets a tc-prefixed value reach the regex, the tc alternative is dead code; the intended prefix is clearly tb. As written, any tb... address matches the guard, then fails the regex, and btc_address returns a ValidationError.

Reproduction

>>> from validators import btc_address
>>> btc_address("tb1qw508d6qejxtdg4y5r3zarvary0c5xw7kxpjzsx")  # canonical BIP173 testnet
ValidationError(func=btc_address, ...)   # should be True
>>> btc_address("bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4")  # mainnet
True

Fix

-        re.compile(r"^(bc|tc)[0-3][02-9ac-hj-np-z]{14,74}$").match(value)
+        re.compile(r"^(bc|tb)[0-3][02-9ac-hj-np-z]{14,74}$").match(value)

Tests

Added the canonical BIP173 testnet address to the valid-address cases in tests/crypto_addresses/test_btc_address.py. It fails on the current code and passes with the fix; the full file passes (9 tests).