As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which requires creating a multi-module Go project.

Before we can do this, we need to break some dependencies between
packages that don't make sense.

As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which we can start with by removing unnecessary
dependencies on `echo` from the `pkg/codegen` project.

As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which requires creating a multi-module Go project.

Before we can do this, we can make sure that we have set up our Makefile
and `tidy` workflow to be module-aware via steps in [0].

[0]: https://www.jvt.me/posts/2023/08/18/go-multi-module-execute/

As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which requires creating a multi-module Go project.

We can start with the `examples` project, which definitely shouldn't be
pulled by consumers.

The fake module version updates across all files due to the way that
multi-module Go projects work, but should be a one-time update.

As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which requires creating a multi-module Go project.

We can split each of the middleware packages into their own modules,
allowing consumers to pull only the dependences they need.

As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which requires creating a multi-module Go project.

We can migrate `internal/test` to its own module, as it shouldn't be
(nor could it be) pulled by consumers.

The fake module version updates across all files due to the way that
multi-module Go projects work, but should be a one-time update.

As part of #1142, we want to reduce the transitive dependencies of
oapi-codegen, which requires creating a multi-module Go project.

We can move `pkg/testutil` to alleviate any other dependencies the root
module has on web frameworks, and allow this to be used independently.