SG-42277 Fix get_currently_running_api_version() under pip install

[stevelittlefish]

Background

When tk-core is pip-installed into a venv, the package lands in a flat
site-packages/tank/ layout. The native install layout assumed by the code
(install/core/python/tank/ with info.yml two levels up from tank/) is
absent, so pipelineconfig_utils.get_currently_running_api_version()
resolves info.yml to a non-existent <venv>/Lib/info.yml,
_get_version_from_manifest swallows the error, and "unknown" is returned.

This silently breaks Sgtk.version and any code path that compares the
currently-running core version against a config's required core version
(e.g. PipelineConfiguration.__init__ at
pipelineconfig.py:73).

Related to the broader pip-install layout cleanup in #1091.

Fix

Add an importlib.metadata.version("sgtk") fallback in
get_currently_running_api_version(). The info.yml read remains the
primary source — only when it returns "unknown" do we consult the
installed sgtk distribution metadata. PEP 440 strips the leading v, so
the fallback re-adds it to match the info.yml format and the docstring's
documented return shape ('v1.2.3').

Behavior:

Install layout	info.yml present?	sgtk dist-info present?	Returned value
Source / native	yes	n/a	manifest value (e.g. "HEAD", "v0.23.8")
Pip install	no	yes	"v" + dist_version (e.g. "v0.23.8")
Bare copy / no metadata	no	no	"unknown" (preserves original contract)

_get_version_from_manifest and get_core_api_version(core_install_root)
are unchanged. The latter has different semantics — "what version is at
this core install root?" — where "unknown" is the correct answer when
the manifest at that root is missing.

Out of scope (still broken under pip; can be addressed separately):
Sgtk.documentation_url, core hook resolution, the TANK_CURRENT_PC skip
in tank/__init__.py, and setup_project_core's binary copying. Each of
those reads files (hooks/, schema/, setup/) that aren't shipped to
site-packages/.

Testing

Three layers:

• Unit tests in tests/core_tests/test_pipelineconfig_utils.py —
  new TestGetCurrentlyRunningApiVersion class with three mocked tests:
  manifest present (fallback not consulted), manifest missing → fallback
  succeeds, both missing → "unknown". Hermetic, fast.
• tests/integration_tests/pip_install.py — extended
  test_pip_install_and_import to assert
  get_currently_running_api_version() returns a non-"unknown" vX.Y.Z
  string after a real pip install into a fresh venv.
• tests/integration_tests/pip_install_bootstrap.py — added
  test_get_currently_running_api_version_in_simulated_pip_layout
  asserting the function returns a string and does not raise in the
  simulated flat layout. Assertion is intentionally permissive:
  importlib.metadata reads from the runtime Python's site-packages,
  not the sys.path-prepended simulated copy, so a developer who also
  has sgtk pip-installed in their dev Python will get the dist version
  rather than "unknown".

Note: Draft. The first commit on this branch contains the new tests
only — the fix in pipelineconfig_utils.py will land in a follow-up
commit. CI on this commit is expected to fail
test_falls_back_to_dist_metadata_when_manifest_missing and the
extended test_pip_install_and_import, demonstrating that the new
tests catch the bug. CI should go green once the fix is added.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.43%. Comparing base (5d4ea39) to head (e0db8bc).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1096      +/-   ##
==========================================
- Coverage   79.43%   79.43%   -0.01%     
==========================================
  Files         198      198              
  Lines       20749    20756       +7     
==========================================
+ Hits        16482    16487       +5     
- Misses       4267     4269       +2     

Flag	Coverage Δ
Linux	78.90% <100.00%> (+<0.01%)	⬆️
Python-3.10	79.25% <100.00%> (+<0.01%)	⬆️
Python-3.11	79.15% <100.00%> (+<0.01%)	⬆️
Python-3.13	79.15% <100.00%> (+<0.01%)	⬆️
Python-3.9	79.21% <100.00%> (-0.01%)	⬇️
Windows	78.93% <100.00%> (-0.01%)	⬇️
macOS	78.91% <100.00%> (+<0.01%)	⬆️

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[carlos-villavicencio-adsk]

LGTM

[julien-lang]

Not great that we compare to string unknown. It would be better to use Python None.

Also, can we return success sooner. (reverse the condition).

[julien-lang]

Please bring specific expcetion if possible

[julien-lang]

can we import at the beginning of the file?

            import importlib.metadata

Then

           return importlib.metadata.version("sgtk")