$ llm codec: Cohere TIMEOUT and Bedrock malformed_* stops are served and billed as in 1.5.5

[MattJackson]

What. The Cohere reader mapped finish_reason: TIMEOUT, and the Bedrock reader mapped stopReason: malformed_model_output | malformed_tool_use, to IrStopReason::Error. Through exchange::reply::wire::generation_failed that turned a translated buffered answer into a 502 that still carried its usage, and charged a lane fault. A Cohere TIMEOUT stream also raised an in-band error event. This PR restores 1.5.5: all three read as Other, so the answer is served and billed as a served answer.

Why. Row-159 audit, plane-llm L2#5 (HIGH). The 1.5.5 source is v1.5.5 crates/busbar/src/proto/cohere/mod.rs:179-191 and crates/busbar/src/proto/bedrock/mod.rs:705-716 (_ => S::Other). Nothing signs the change. The fidelity rule says "Billing never moves". §7 and #77 keep the money path at 1.5.5. CHANGELOG 1.6.0 (the "stream that dies mid-flight" entry) registers only Cohere's generic ERROR, and only on streams.

RED-able tests.

• cohere/tests/ir_mapping_tests.rs::timeout_is_served_and_billed_as_in_1_5_5: generation_failed("cohere", …) is false, the usage is 3/1, and the stream has no Error event.
• bedrock/tests/ir_mapping_tests.rs::bed10_context_window_and_malformed_stop_reasons_map: both malformed_* read Other and generation_failed("bedrock", …) is false.
• cohere/tests/tests.rs: read_cohere_stop_reason("TIMEOUT") == Other.

Not changed: the generic Cohere ERROR (registered), and Bedrock model_context_window_exceeded → MaxTokens (a MEDIUM translation item, not money). No ledger, oracle cell or ceiling changes.

[MattJackson]

row 155 B2 (#974) edits crates/busbar-plane-llm/src/codec/{bedrock,cohere}/mod.rs at fn claims and the DECL quota_exceeded_status / auth_failure_status_and_kind rows; disjoint from this PR's hunks.