fix(version): close orphan docstring so 0.13.0 section parses

CI on PR #53 (`test (3.10/3.11/3.12)` all FAIL, coverage 0.05%)
surfaced a SyntaxError collected in `src/nullrun/__version__.py`
line 86:

  v3.13 / 0.13.0 (2026-07-04) — drift-fixes release: closes the SDK-side
                         ^
  SyntaxError: leading zeros in decimal integer literals are not
  permitted; use an 0o prefix for octal integers

Root cause: in the 0.13.0 release commit I closed the module
docstring with `"""` after the 0.12.2 section and then started
writing the 0.13.0 section as if it were still inside a docstring —
Python parsed `v3.13 / 0.13.0 (2026-07-04) — drift-fixes ...` as
module-level expressions, barfed on `(2026-07-04)` (the `07` is a
leading-zero integer literal — illegal in Python 3), and the rest
of the test collection cascade-failed with 64 collection errors.
Coverage hit 0.05% because pytest couldn't even collect, not
because tests regressed.

Fix: drop the orphan `"""` between the 0.12.2 and 0.13.0 sections
and replace it with a `---` separator (the docstring stays open
all the way to the module-final `"""` above `__version__ = "0.13.0"`).

Verified locally:
  $ python -c "import src.nullrun.__version__; print(__version__.__file__)"
  (no SyntaxError, imports cleanly)

`grep -c '"""' src/nullrun/__version__.py` now reports 2
(open + close), as expected for a single module docstring.

Author: maltsev-dev

src/nullrun/__version__.py

@@ -81,7 +81,8 @@
 1.0.0 keep working unchanged. Pinning unchanged:
 SDK_MIN_VERSION_FOR_V3 = "0.12.0". Recommended upgrade
 path: 0.12.1 -> 0.12.2.
-"""
+
+---
 
 v3.13 / 0.13.0 (2026-07-04) — drift-fixes release: closes the SDK-side
 items left over from the docs-vs-code audit captured in