fix: Resolve critical bugs - file handle leaks and IndexError issues

Fixed multiple critical bugs identified during comprehensive code audit:

**Critical Fixes:**
- Fix file handle leaks in SDK client upload methods (sync and async)
  - Use context managers to ensure file handles are properly closed
  - Affects: sdk/src/fuzzforge_sdk/client.py lines 397, 484

**High Priority Fixes:**
- Fix IndexError in OSS-Fuzz stats parsing when accessing array elements
  - Add bounds checking before accessing parts[i+1]
  - Affects: workers/ossfuzz/activities.py lines 372-376

- Fix IndexError in exception handling URL parsing
  - Add empty string validation before splitting URL segments
  - Prevents crash when parsing malformed URLs
  - Affects: sdk/src/fuzzforge_sdk/exceptions.py lines 419-426

**Medium Priority Fixes:**
- Fix IndexError in Android workflow SARIF report parsing
  - Check if runs list is empty before accessing first element
  - Affects: backend/toolbox/workflows/android_static_analysis/workflow.py line 270

All fixes follow defensive programming practices with proper bounds checking
and resource management using context managers.

workers/ossfuzz/activities.py

@@ -368,11 +368,11 @@ def parse_fuzzing_stats(stdout: str, stderr: str, engine: str) -> Dict[str, Any]
                 # Example: #8192 NEW    cov: 1234 ft: 5678 corp: 89/10KB
                 parts = line.split()
                 for i, part in enumerate(parts):
-                    if part.startswith("cov:"):
+                    if part.startswith("cov:") and i+1 < len(parts):
                         stats["coverage"] = int(parts[i+1])
-                    elif part.startswith("corp:"):
+                    elif part.startswith("corp:") and i+1 < len(parts):
                         stats["corpus_entries"] = int(parts[i+1].split('/')[0])
-                    elif part.startswith("exec/s:"):
+                    elif part.startswith("exec/s:") and i+1 < len(parts):
                         stats["executions_per_sec"] = float(parts[i+1])
                     elif part.startswith("#"):
                         stats["total_executions"] = int(part[1:])