fix(sdk): normalize state manager base URL separators

[breken-ai]

Fixes #642.

What goes wrong

StateManager(namespace, state_manager_uri="http://localhost:8000/") builds http://localhost:8000//v0/namespace/<ns>/graph/<g>: the three endpoint helpers interpolate {base}/{version}/… and nothing normalises the base, so a URI with a trailing slash, from the constructor or from EXOSPHERE_STATE_MANAGER_URI, gets a doubled separator that some servers and proxies reject.

The change

One normalisation in _set_config_from_env(), after the environment fallback, so explicit and environment configuration behave the same: trailing separators are stripped from the resolved string. Scheme, authority, port and a deployment prefix (https://example.test/api/ → …/api) are preserved; a missing URI stays None rather than becoming a valid-looking string. Nothing else about URL handling changes. The README's parameter note says the slash is accepted.

Tests

python-sdk/tests/test_statemanager_base_uri.py: seven base shapes (with and without a trailing slash, /api/ prefix, IPv6 authority, repeated slashes) × the three endpoint helpers × explicit and environment configuration, plus the missing-URI case.

• Before the change: 30 failed, 13 passed (every trailing-slash shape, every helper, both configuration paths).
• After: 43 passed; full SDK suite 217 passed; ruff check . clean.

Evidence record

Repository / issue:        FailproofAI/runtime #642
Upstream SHA / patch SHA:  2db4b154 / 8550f7c
Issue ownership:           open, unassigned, no linked or competing PR (checked 2026-09-12 21:41 UTC, 37 open PRs)
Reproducer:                uv run pytest tests/test_statemanager_base_uri.py → 30 failed, 13 passed on 2db4b154
Patched:                   same command → 43 passed; uv run pytest → 217 passed; uv run ruff check . → clean
Checks not executed:       loopback HTTP integration under a prefix (no server in this change)