fix(wasm-utxo): enable drop ExtParams in fromStringDetectType

[veetragjain]

Descriptor.fromStringDetectType was rejecting taproot descriptors containing
payload_drop or r:older because its outer parse_descriptor call used default
ExtParams without the drop flag.

Swap parse_descriptor for parse_descriptor_ext(..., ExtParams::sane().drop())
to match the pattern used elsewhere in the file. ExtParams::sane().drop() is a
strict superset of ExtParams::sane(), so the change is purely additive — every
descriptor that parsed before still parses now.

Adds TS tests in test/sbtc.ts covering fromStringDetectType with payload_drop
and r:older.

Ticket: CSHLD-815

[linear-code]

CSHLD-815