fix(deps): relax install_requires pins to compatible ranges (VC-53626)

[SahilWikhe-sw]

Summary

• Replace hard-pinned (==) install_requires entries in setup.py with compatible-range constraints (>=current,<next-major) for all 6 deps.
• Addresses VC-53626 (SC-006 / CWE-1395): hard pins on a published library prevent downstream consumers from upgrading transitive dependencies and cause resolver conflicts.
• requirements.txt is left as exact pins (development reproducibility); only install_requires was changed.

Change

- install_requires=['requests==2.32.4', 'python-dateutil==2.8.2', 'six==1.17.0',
-                   'cryptography==45.0.7', 'ruamel.yaml==0.18.13', 'pynacl==1.5.0']
+ install_requires=['requests>=2.32.4,<3', 'python-dateutil>=2.8.2,<3', 'six>=1.17.0,<2',
+                   'cryptography>=45.0.7,<46', 'ruamel.yaml>=0.18.13,<0.19', 'pynacl>=1.5.0,<2']

Test plan

• pip install --dry-run . resolves all ranges cleanly (verified locally)
• Lower bounds preserve currently pinned floors — no downgrade for consumers already on these versions
• CI pipeline passes

Jira: VC-53626