Running tox tests locally is painfully slow (for slow internet connections)

When running tox tests for an instrumentation dependencies to the core repo are currently resolved/installed via pip, which clones the core repo to a temporary local folder.

A single instrumentation usually requires multiple packages from the core repo. E.g. running tox -e py39-test-instrumentation-botocore requires: opentelemetry-api, opentelemetry-semantic-conventions, opentelemetry-instrumentation, opentelemetry-sdk, and opentelemetry-test.
For each of these dependencies, pip will separately clone the core repo. Currently, the core repo is ~75MB in size. For slow internet connections (~1MB/s) a single clone operation can already take up to 1min. So for a single test run to complete that would already be about 5min+.

It might not be that noticeable in CI but i guess cloning the core repo for every dependency also negatively impacts the CI build time since this actually multiplies by test and by runtime.

The reported entry point is tox -e py39-test-instrumentation-botocore; begin by tracing how this environment installs the five core-repository packages with pip. Compare local and CI behavior, then verify that one instrumentation run no longer repeats the core-repository clone for each dependency.