Fix/update string type conditions

[Hamedblue1381]

Context

This PR closes issue #14.

The problem was:

• The TypeScript generator threw an error if encoding was not "ascii".
• We were allowing string as a type, which should not be valid.

What I did

• ❌ Removed support for string as valid types.
• ✅ Updated the generator to use sia.addString{N|8|16|32|64} and sia.readString{N|8|16|32|64} or addAscii{number} and readAscii{number} based on the string type, not the encoding.
• For Python, Go, and C++ generators, the encoding field is now ignored, as their respective SIA libraries do not have specific functions or arguments related to encodings.
• Refactor the code abit with suffix map namings and usage of switch case for more readability

Tests

• ✅ Updated test mock to make sure string now throw errors.
• ✅ Confirmed that string8, string16, string32, string64 all generate correct code.

Notes

• Users must now use valid types: stringN, string8, string16, string32, or string64.
• The encoding field is ignored in the Python, Go, and C++ generators — type controls everything now.

[Hamedblue1381]

I havent figured out what function names for stringN must be used, WIP

[Hamedblue1381]

requires asciiN and stringN to be merged