feat: move mockprock package into src/ layout

Move the package from top-level mockprock/ to src/mockprock/ per the
modernization standard. Update pyproject.toml (add where = ["src"],
switch to source_pkgs for coverage) and tox.ini (point pylint/isort
at src/mockprock).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: farhan

pyproject.toml

@@ -47,6 +47,7 @@ get-dashboard = "mockprock.commands:get_url"
 Repository = "https://github.com/openedx/mockprock"
 
 [tool.setuptools.packages.find]
+where = ["src"]
 exclude = ["tests*", "*.tests", "*.tests.*"]
 
 [tool.setuptools.package-data]
@@ -114,7 +115,7 @@ addopts = "--cov mockprock --cov-report term-missing --cov-report xml"
 # https://coverage.readthedocs.io/en/latest/config.html
 [tool.coverage.run]
 branch = true
-source = ["mockprock"]
+source_pkgs = ["mockprock"]
 omit = [
     "*/tests/*",
     "*/__pycache__/*",