Decode an inscription-ID field value: 32-byte txid (internal order) plus up
to 4 little-endian index bytes. Mirrors ord's InscriptionId::from_value
(inscription.rs @ 7effaaaf): a trailing zero index byte is rejected ONLY for
variable-width encodings (1-3 index bytes); the fixed-width 4-byte form is
accepted with trailing zeros (so 32+4 bytes with a 0x00 high byte is valid).
Decode an inscription-ID field value: 32-byte txid (internal order) plus up to 4 little-endian index bytes. Mirrors ord's InscriptionId::from_value (inscription.rs @ 7effaaaf): a trailing zero index byte is rejected ONLY for variable-width encodings (1-3 index bytes); the fixed-width 4-byte form is accepted with trailing zeros (so 32+4 bytes with a 0x00 high byte is valid).