[Python] Base SDK Store http span in context variable

[selcukcihan]

Description

• Related issue https://linear.app/serverless/issue/SC-742/python-sdk-thread-safety
• I've identified another potential for a race-condition. This will make sure each http spans are stored as context variables and do not interfere with each other.

Testing done

• Reproduced the problem in a unit test and fixed.
• Integration tested.

    ✔ success-v3-8 (46964ms)
    ✔ success-v3-9 (6081ms)
    ✔ success-sampled
    ✔ error-v3-8
    ✔ error-v3-9 (1810ms)
    ✔ error_unhandled-v3-8
    ✔ error_unhandled-v3-9
    ✔ sdk-v3-8
    ✔ sdk-v3-9
    ✔ sdk-dev-mode
    ✔ dashboard-v3-8 (403ms)
    ✔ dashboard-v3-9
    ✔ http_requester-http
    ✔ http_requester-https
    ✔ aiohttp_requester-http
    ✔ aiohttp_requester-https (1195ms)
    ✔ flask_app

[selcukcihan]

@medikoo ready for review please 🙏