[3.13] gh-135944: Add a "Runtime Components" Section to the Execution Model Docs (gh-135945) (#139510)

* gh-135944: Add a "Runtime Components" Section to the Execution Model Docs (gh-135945)

The section provides a brief overview of the Python runtime's execution environment.  It is meant to be implementation agnostic,
(cherry picked from commit 46a1f0a9ff6e7cbea111dcb35e7aced1a7a3f3dc)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

* concurrent.interpreters was added to Python 3.14

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Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>
Co-authored-by: T. Wouters <thomas@python.org>
Co-authored-by: Kumar Aditya <kumaraditya@python.org>
Co-authored-by: Victor Stinner <vstinner@python.org>