test: remove noisy print statements

[j-kon]

Summary

Remove unconditional debug/print output from a small set of Rust test files where the assertions already provide enough signal on failure.

Scope

This change is intentionally limited to test cleanup in:

• bdk-ffi/src/tests/descriptor.rs
• bdk-ffi/src/tests/keys.rs
• bdk-ffi/src/tests/bitcoin.rs

I left tx_builder.rs unchanged in this pass because those prints are mixed into live-network and failure-diagnostic paths, so I wanted to keep the scope conservative.

What changed

• removed println! calls from descriptor template/address-data/psbt-related tests where they were only adding noise on success
• removed dbg! calls from key tests
• kept test behavior the same
• replaced one print-driven sanity check in test_to_address_data with explicit variant assertions

Verification

• cargo fmt --check
• cargo test descriptor
• cargo test psbt
• cargo test test_to_address_data
• cargo test test_from_str_inner

[thunderbiscuit]

One tiny fix I'd like to see and this is ready to go! Thanks for working on this.

[thunderbiscuit]

I'm not sure why we're testing the length of the unknown field here but let's remove this line while we're at it!

[j-kon]

Thanks, I removed that extra unknown.len() assertion from test_psbt_input_length and force-pushed the update.

I re-ran:

• cargo fmt --check
• cargo test test_psbt_input_length
• cargo test psbt

[thunderbiscuit]

ACK f8f8bfd.