chore(tesla): removing warnings and clean up test cases

[yordis]

Context

Doing some grunt work, removing the warning from the test environment and clean up other things around the test cases

..     warning: redefining module Tesla.Middleware.OpenTelemetryTest.TestClient (current version defined in memory)
     │
 227 │       defmodule TestClient do
     │       ~~~~~~~~~~~~~~~~~~~~~~~
     │
     └─ test/middleware/opentelemetry_tesla_middleware_test.exs:227: Tesla.Middleware.OpenTelemetryTest.TestClient (module)

.     warning: redefining module Tesla.Middleware.OpenTelemetryTest.TestClient (current version defined in memory)
     │
 227 │       defmodule TestClient do
     │       ~~~~~~~~~~~~~~~~~~~~~~~
     │
     └─ test/middleware/opentelemetry_tesla_middleware_test.exs:227: Tesla.Middleware.OpenTelemetryTest.TestClient (module)

.     warning: redefining module Tesla.Middleware.OpenTelemetryTest.TestClient (current version defined in memory)
     │
 227 │       defmodule TestClient do
     │       ~~~~~~~~~~~~~~~~~~~~~~~
     │
     └─ test/middleware/opentelemetry_tesla_middleware_test.exs:227: Tesla.Middleware.OpenTelemetryTest.TestClient (module)

.     warning: redefining module Tesla.Middleware.OpenTelemetryTest.TestClient (current version defined in memory)
     │
 227 │       defmodule TestClient do
     │       ~~~~~~~~~~~~~~~~~~~~~~~
     │
     └─ test/middleware/opentelemetry_tesla_middleware_test.exs:227: Tesla.Middleware.OpenTelemetryTest.TestClient (module)

.     warning: redefining module Tesla.Middleware.OpenTelemetryTest.TestClient (current version defined in memory)
     │
 227 │       defmodule TestClient do
     │       ~~~~~~~~~~~~~~~~~~~~~~~
     │
     └─ test/middleware/opentelemetry_tesla_middleware_test.exs:227: Tesla.Middleware.OpenTelemetryTest.TestClient (module)

.    warning: redefining module Tesla.Middleware.OpenTelemetryTest.TestClient (current version defined in memory)
    │
 98 │       defmodule TestClient do
    │       ~~~~~~~~~~~~~~~~~~~~~~~
    │
    └─ test/middleware/opentelemetry_tesla_middleware_test.exs:98: Tesla.Middleware.OpenTelemetryTest.TestClient (module)