Unify SONiC breakout mode selection across name formats

[berendt]

detect_breakout_ports mapped subport speed to breakout mode with two independent tables: the NetBox EthX/Y/Z path supported 4x10G, 4x25G, 4x50G, 4x100G and 4x200G, while the SONiC EthernetX path only knew 4x25G and 4x50G. A 4x10G breakout of a 40G/100G port (e.g. on an Edgecore AS7726-32X) was therefore silently dropped when the interfaces are named in the SONiC format.

Move the speed-to-mode table into the shared constant BREAKOUT_MODE_BY_SPEED and use it at both detection sites. The EthernetX path keeps its <= 50G group membership filter, so it now covers 4x10G, 4x25G and 4x50G; 4x100G stays with the dedicated 400G branch that matches ports spaced by two.

Closes #2482

🤖 Generated with Claude Code

https://claude.ai/code/session_016mkKSzFNC2UsAfgyQqTJxw

[sourcery-ai]

Hey - I've left some high level feedback:

• The new BREAKOUT_MODE_BY_SPEED dict is keyed in Mbps (e.g. 10000), but the added test parametrization uses values like 10_000_000, which suggests a unit mismatch between the production code and tests that should be aligned or clarified.
• Since the SONiC EthernetX path is constrained to <= 50G, consider either constraining BREAKOUT_MODE_BY_SPEED to the same range or adding a short comment where it is declared to clarify why 100G/200G entries exist but are only used by the NetBox path.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new `BREAKOUT_MODE_BY_SPEED` dict is keyed in Mbps (e.g. `10000`), but the added test parametrization uses values like `10_000_000`, which suggests a unit mismatch between the production code and tests that should be aligned or clarified.
- Since the SONiC `EthernetX` path is constrained to `<= 50G`, consider either constraining `BREAKOUT_MODE_BY_SPEED` to the same range or adding a short comment where it is declared to clarify why 100G/200G entries exist but are only used by the NetBox path.

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