Fix #1745 - Throw on multiple configs

[WebReflection]

Description

This MR fixes #1745 by throwing errors in these conditions:

• multiple <py-config> or <mpy-config> found on the page
• both <py-config> and <script type="py" config="file.toml"> found on main
• different <script type="py" config="a.toml"> and <script type="py" config="b.toml"> configs found on main

TODO

• add integration tests once agreed this is currently what we want, as the discussion never had an OK

Changes

• make the config crawler more greedy to prevent possible errors later on
• add smoke tests to verify all cases are covered

Checklist

• All tests pass locally
• I have updated CHANGELOG.md
• I have created documentation for this(if applicable)

[fpliger]

lgtm! 👍