Function toMrzField9

Public algorithm primitives. Tree-shakable subpath: nationid/algorithms.

Each function is a pure mathematical primitive with cited spec.

toMrzField9(printed: string): string
Right-pad a printed passport number to the 9-char MRZ field with <. Useful when the issued number is shorter than 9 chars.

Lowercase letters are uppercased before validation, so callers do not need to pre-normalize case.
Parameters
- printed: string
  The number as printed on the data page (1..9 chars).
Returns string
A 9-char string in the MRZ alphabet, right-padded with <.
Throws
ICAO_TOO_LONG if printed exceeds 9 chars.

Throws
ICAO_INVALID_CHAR if printed contains characters outside [0-9A-Za-z] (filler < is added by the function, not accepted as input).
Example
```
import { toMrzField9 } from "nationid/algorithms";

toMrzField9("L898902C"); // "L898902C<"
toMrzField9("abc123");   // "ABC123<<<"
```
- Defined in algorithms/icao-9303.ts:132