fix: num64 == "long" generates broken helper files

[ahm23]

When configured to use Long for 64-bit numbers instead of bigint, certain helper files like helper-func-types.ts are still being generated to import ./binary and use BinaryReader/BinaryWriter for param type definitions, where they shouldn't be.

src/types/binary.ts, src/types/utf8.ts, and src/types/varint.ts are not even generated when configured to use Long for 64-bit numbers, so while it's not only incorrect, it also causes build issues in packages importing a package generated using telescope because of the missing imports.

This change makes the helper templates use the right encoding/decoding mechanisms, and removes broken imports:

• num64: "bigint" continues to use BinaryReader / BinaryWriter from ./binary
• num64: "long" now uses _m0.Reader / _m0.Writer from protobufjs/minimal as it should