RTLD_GLOBAL causes symbol conflicts with other libraries

## Problem

Decord uses `ctypes.RTLD_GLOBAL` when loading `libdecord.so`, which exports all symbols (including FFmpeg/libav) into the global namespace. This causes symbol conflicts with other libraries that use similar dependencies, leading to crashes.

## Minimal Reproduction

```python
import decord
import wgpu

adapter = wgpu.gpu.request_adapter_sync()
```
```
Segmentation fault (core dumped)
```

**Expected behavior:**
Both libraries work together without crashes.

## Root Cause

The issue is in `python/decord/_ffi/base.py:39`:

```python
def _load_lib():
"""Load libary by searching possible path."""
lib_path = libinfo.find_lib_path()
os.environ['PATH'] += os.pathsep + os.path.dirname(lib_path[0])
lib = ctypes.CDLL(lib_path[0], ctypes.RTLD_GLOBAL) # <---
# DMatrix functions
lib.DECORDGetLastError.restype = ctypes.c_char_p
return lib, os.path.basename(lib_path[0])
```

## Additional Context

- **Platform:** Linux
- **Python:** 3.13
- **Decord:** Latest from pip
- **Other library tested:** wgpu