#41762 introduced new infrastructure for sharing code in `aes_common.rs`
among AES algorithms.
This patch makes AES-CTR algorithm adopt the new infrastructure, by
moving the relevant code away from `aes_operation.rs` to its own
`aes_ctr_operation.rs`, with refactoring for adaptation.
Testing: Refactoring. Existing tests suffice.
Fixes: Part of #41763
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Signed-off-by: Kingsley Yung <kingsley@kkoyung.dev>