[skuirrels]

Summary

• Duplicated port codes no longer throw. Twelve codes have two port-list records and no UN/LOCODE position (INNSA, PHDVO, IDPLM and others). Resolution called the throwing GetByCode overload, so every movement and Locate through them failed, whatever the mode. Port-to-port CalculateRoute threw for all 38 duplicated codes, CAVAN included. A new SelectPortRecord takes the record nearest the UN/LOCODE position or, without one, the terminal record of a group lying within 50 km. It throws only when the records are further apart.
• Port-list namesakes are rejected. When UN/LOCODE lists a code without a position, the last fallback took the port-list record even when it named a different place: Locate("USLBE") returned Laguna Beach, California, not Latrobe, Pennsylvania. The names must now agree, allowing for spelling variants such as Haerbin and Harbin, and Helsinki and Helsingfors. 27 codes now throw an ArgumentException naming both places, 21 of them in the United States.

Behaviour changes to note

• CNSWA and CNWUX now throw: UN/LOCODE files them as airports, and the ports are CNSTG and CNWXS. INCOO (Kundapur and Coondapur) is spelt too differently to match.

Testing

• dotnet test -m:1 -nr:false: 580 passed on net8.0 and net10.0.
• New tests cover rejected namesakes, kept spelling variants, every duplicated code resolving, a Nhava Sheva sea movement, and code-only routes for INNSA and CAVAN.
• Resolved all 3,924 port-list codes: exactly 27 rejected as namesakes, no other failures.