Memory leak in sqlite3.Connection.load_extension()

Bug report

Bug description:

Public issue regarding the issue found by @sushi-gif. Here is a summary of the discussion:
The function sqlite3.Connection.load_extension() has a minor memory leak that occurs when SQLite throws an error while loading an extension (sqlite3_load_extension). According to SQLite specifications, the buffer of the error message must be freed manually after use. The attached PR fixes the issue.

Reproduction code:

import sqlite3

cx = sqlite3.connect(":memory:")
cx.enable_load_extension(True)

for _ in range(1000000):
    try:
        cx.load_extension("does_not_exist")
    except sqlite3.Error:
        pass

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-154110

从 sqlite3.Connection.load_extension() 的实现开始，跟踪其对 sqlite3_load_extension 的调用。使用提供的重复失败加载复现来检查错误路径，并验证报告的内存泄漏已修复，同时不改变扩展成功加载的行为。