emit number(0) (offset(0)??) for instructions like "XOR EAX, EAX"

see https://github.com/mandiant/capa-rules/pull/993#issuecomment-2711090176

Start by reading the linked capa-rules pull request comment, which contains the only reported context. Trace how instruction operands are represented and emitted for the XOR EAX, EAX example, then clarify whether the expected result is number(0) or offset(0). Done means the intended zero-valued representation is emitted consistently and covered by a relevant test.

Written by the indexing model from the issue text.