The `Env` function retrieves the value of an environment variable and provides a fallback value if the variable is not set.

The function `EnvWithConverter` retrieves an environment variable value and converts it to a specified type using a provided converter function.

The type EnvValueType represents a value that can be an integer, unsigned integer, floating-point number, boolean, string, or time.

The FloatType interface represents either a float32 or a float64 type.

The above type defines an interface that can be implemented by any integer type in Go.

The above type defines an interface that can be implemented by any unsigned integer type in Go.