fix(clippy): PowerStatusV2::to_v1 takes self by value

[cmd0s]

cargo clippy --all-targets -- -D warnings (the CI gate) fails on main after the v2 decoder merge (PR #1):

error: methods with the following characteristics: (`to_*` and `self` type is `Copy`) usually take `self` by value
  --> src/proto/payloads.rs:314

PowerStatusV2 is Copy, so to_v1 should take self by value per clippy::wrong_self_convention. Both call sites (dispatcher.rs:77, the round-trip test) pass an owned/Copy value, so they are unaffected.

Verified locally: cargo clippy --all-targets -- -D warnings clean, cargo fmt --check clean, 82/82 tests pass.

The published v2.1.0 release binary is unaffected (behaviour identical; release.yml does not run clippy). This only greens main CI.