SG-42625 Fix tank_vendor imports for pip installations and developer scripts

[eduardoChaucaGallegos]

Two related fixes for import failures introduced by the pkgs.zip architecture in tk-core v0.23.x.

Fix 1 - Developer scripts use sys.path.insert instead of append

The developer scripts used sys.path.append() to add the local tk-core, but
append() puts it at the end of sys.path, so any sgtk installed in
site-packages takes precedence and fails because it lacks pkgs.zip.

Changed to sys.path.insert(0, ...) in bake_config.py, build_plugin.py and
populate_bundle_cache.py.

Fix 2 - Add install_requires to setup.py

When sgtk is installed via pip, the requirements/ directory (containing
pkgs.zip) is not included. The tank_vendor import hook falls back to loading
packages from the Python environment, but they are not installed because
setup.py had no install_requires.

Added get_install_requires() that reads dependencies from
requirements/<python_version>/requirements.txt, keeping versions in sync
with pkgs.zip.

Testing

• Created a fresh venv, ran pip install -e .
• Verified import sgtk works
• Verified from tank_vendor.shotgun_api3 import Shotgun works
• Verified from tank_vendor.shotgun_api3.lib import httplib2 works

Fixes for issues: #1090

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.42%. Comparing base (28f457c) to head (25dabb0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1091      +/-   ##
==========================================
- Coverage   79.43%   79.42%   -0.01%     
==========================================
  Files         198      198              
  Lines       20751    20751              
==========================================
- Hits        16483    16481       -2     
- Misses       4268     4270       +2     

Flag	Coverage Δ
Linux	78.89% <ø> (ø)
Python-3.10	79.24% <ø> (ø)
Python-3.11	79.14% <ø> (-0.01%)	⬇️
Python-3.13	79.14% <ø> (ø)
Python-3.9	79.21% <ø> (-0.01%)	⬇️
Windows	78.92% <ø> (-0.01%)	⬇️
macOS	78.90% <ø> (ø)

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[carlos-villavicencio-adsk]

Hi @eduardoChaucaGallegos , can you also check if this case is covered here?

[julien-lang]

One thing I don't understand in this PR is why those issues sudently created problems? What was the cause and why?

[julien-lang]

LGTM!

[eduardoChaucaGallegos]

One thing I don't understand in this PR is why those issues sudently created problems? What was the cause and why?

Good question - full context is in SG-42625, but here's the short version.

These bugs are latent - they always existed but only became visible as pip installs of sgtk are becoming more common outside the standard Toolkit/DCC workflow. Both issues were introduced (or exposed) by the task that reorganized third-party dependencies into requirements/<python_version>/pkgs.zip.

Two independent root causes:

1. Developer scripts used sys.path.append instead of sys.path.insert(0, ...)
If sgtk was already pip-installed, Python would find it in site-packages first and the scripts would silently run against the wrong tank module.

2. setup.py had no install_requires
pkgs.zip is not included in a pip install and setup.py was never updated to declare the dependencies. So pip would install successfully but fail at runtime with ModuleNotFoundError: No module named tank_vendor.shotgun_api3. The fix reads pinned versions from the existing requirements/<python_version>/requirements.txt to stay in sync with pkgs.zip.