Fix duplicate slash URL handling for 25.8

[benflexcompute]

Summary

• Normalize Flow360 environment URL construction so leading path slashes do not create duplicate slash API paths.
• Remove known leading slash folder API paths.
• Constrain Requests to the 2.32 patch line.
• Add focused URL normalization tests.

Verification

• PYTHONDONTWRITEBYTECODE=1 /disk2/ben/Flow360/.venv/bin/python -m pytest tests/test_environment.py -q -p no:cacheprovider
• Forced local repro with requests==2.34.2: prod and preprod folder requests used single-slash URLs and RestApi.get succeeded.

Note: poetry check --lock still fails on the existing unrelated pyswarms docs extra issue, but no longer reports stale lock metadata.

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Note

Medium Risk
Touches how all REST URLs are built and folder API paths; wrong joining could break API calls, though behavior is covered by new tests.

Overview
Fixes double-slash API URLs when environment base URLs end with / and REST paths start with / (or the opposite). EnvironmentConfig URL helpers now join bases and paths with normalized slashes; folder listing code uses v2/items and v2/folders without a leading slash.

requests is capped to the 2.32 patch line (>=2.32.4,<2.33.0) with an updated lockfile. New tests cover slash normalization for environment URLs and RestApi paths.

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