Validate field numbers

[eigenein]

https://developers.google.com/protocol-buffers/docs/proto3#assigning-field-numbers

The smallest field number you can specify is 1, and the largest is 2²⁹ - 1, or 536,870,911. You also cannot use the numbers 19000 through 19999 (...), as they are reserved for the Protocol Buffers implementation...