test: activate the full e2e (browser-driving) suite + add fetch --force

The 138 @pytest.mark.e2e tests were doubly inactive: deselected by addopts AND
skipped without a cached binary — and 3 of the 6 per-file firefox_binary
fixtures silently ignored INVPW_BINARY_PATH, so they'd test whatever was cached
even when you pointed the suite elsewhere (a false-confidence trap).

- Centralize firefox_binary into conftest.py (env INVPW_BINARY_PATH → cache →
  skip); delete the 6 duplicates. Unify test_webrtc_realness onto the same env.
- scripts/run_e2e.py: one command that runs ALL e2e against a chosen binary,
  with reruns so an under-load interaction flake (dblclick/hover pass 3/3 in
  isolation) self-heals while a real break fails every attempt. The webrtc e2e
  fake a TCP-only SOCKS locally, so the suite is offline. This is the MANDATORY
  pre-release browser gate (local — hosted runners are too interaction-flaky).
- Running the suite against firefox-9 surfaced a real gap: `invisible_playwright
  fetch --force` was unrecognized (the subparser took no args) though the e2e
  test + docstring expect it. Implement it: drop the cached version dir, refetch.
- Add pytest-rerunfailures + playwright to the dev extras.

Baseline against firefox-9: 136 passed, 1 skipped (linux_only on win host),
1 was the --force gap now fixed.

tests/test_e2e.py

@@ -8,33 +8,9 @@ handling) do not need a binary and always run.
 """
 from __future__ import annotations
 
-import sys
-
 import pytest
 
 from invisible_playwright import InvisiblePlaywright
-from invisible_playwright.constants import BINARY_ENTRY_REL
-
-
-@pytest.fixture(scope="session")
-def firefox_binary():
-    """Locate the patched Firefox binary or skip the calling test.
-
-    We do NOT trigger a network download here: ``ensure_binary`` would
-    pull a multi-hundred-megabyte archive from a private release,
-    which is not appropriate inside a unit/E2E test run. Instead we
-    look for an already-cached binary; if missing we skip.
-    """
-    if sys.platform not in BINARY_ENTRY_REL:
-        pytest.skip(f"unsupported platform: {sys.platform}")
-    from invisible_playwright.download import cache_dir_for_version
-    entry = cache_dir_for_version() / BINARY_ENTRY_REL[sys.platform]
-    if not entry.exists():
-        pytest.skip(
-            "patched Firefox binary not cached; run `invisible-playwright fetch` "
-            "to enable E2E tests"
-        )
-    return str(entry)
 
 
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