Scrapy-zyte-smartproxy

Use a different stat prefix for [Zyte API](https://docs.zyte.com/zyte-api/get-started.html) [proxy mode](https://docs.zyte.com/zyte-api/usage/proxy-mode.html).

**Full Changelog**: https://scrapy-zyte-smartproxy.readthedocs.io/en/latest/news.html

Fix response handling for [Zyte API](https://docs.zyte.com/zyte-api/get-started.html) [proxy mode](https://docs.zyte.com/zyte-api/usage/proxy-mode.html).

**Full Changelog**: https://scrapy-zyte-smartproxy.readthedocs.io/en/latest/news.html

Detect scenarios where the ``proxy`` ``Request.meta`` key has probably been accidentally copied from an earlier response, warn about it, and fix the value.

The ``Zyte-Client`` header is again sent when using [Zyte API](https://docs.zyte.com/zyte-api/get-started.html) [proxy mode](https://docs.zyte.com/zyte-api/usage/proxy-mode.html), now that Zyte API supports it.

**Full Changelog**: https://scrapy-zyte-smartproxy.readthedocs.io/en/latest/news.html

Fixed support for the proxy mode of [Zyte API](https://docs.zyte.com/zyte-api/get-started.html).

**Full Changelog**: https://scrapy-zyte-smartproxy.readthedocs.io/en/latest/news.html

Support for the upcoming proxy API of [Zyte API](https://docs.zyte.com/zyte-api/get-started.html).

**Full Changelog**: https://scrapy-zyte-smartproxy.readthedocs.io/en/latest/news.html

Support Scrapy 2.6.2. Scrapy 1.4+ is now required.