[BUG][RUST-SERVER] binary strings should not be base64 encoded

The rust-server code generator handles binary and byte string format the same way. Both are base64 encoded automatically while binary strings should not perform this transformation as stated in OAS3.2.

Description

The formats defined by the OAS are:

type	format	Comments
string	byte	base64 encoded characters
string	binary	any sequence of octets

openapi-generator version

Tested with docker image openapitools/openapi-generator-cli with version 4.0.1-SNAPSHOT.

OpenAPI declaration file content or url

responses:
    "200":
      description: "OK"
      content:
        image/png:
          schema:
            type: string
            format: binary

Command line used for generation

docker run --rm -u $(id -u ${USER}):$(id -g ${USER}) -v ${PWD}:/local -w /local openapitools/openapi-generator-cli generate \
    --enable-post-process-file \
    --generate-alias-as-model \
    -i /local/openapi/openapi.yaml \
    -g rust-server \
    -o /local/packages/rust-server \
    -DpackageName=server

Related issues/PRs

Issue #538 mentions binary and byte string but doesn't mention how they should be handled differently.

Suggest a fix

Vec<u8> should be used for binary string instead of swagger::ByteArray.

Start with the rust-server generator output produced from the provided OpenAPI declaration and trace how string formats binary and byte are mapped. Verify the generated response handling against the OAS 3.2 distinction; done means binary uses Vec while byte retains base64 encoding.