refactor: rename downloader instances for consistency across modules

[fllesser]

No description provided.

[github-actions]

类型	PIL 耗时(秒)	HTML 耗时(秒)	渲染所用图片总大小(MB)	PIL 导出图片大小(MB)	HTML 导出图片大小(MB)
微博视频2	0.01269	0.78272	0.01280	0.03541	0.18327
微博视频	0.01476	0.79726	0.01280	0.03432	0.18050
微博纯文2	0.03260	0.89226	0.00605	0.12023	0.35956
微博转发纯文	0.07832	1.12398	0.01724	0.24325	0.71448
微博转发(横图)	0.19170	1.53119	1.26621	0.48412	2.21493
B站转发动态	0.21309	1.58652	0.37278	0.38265	1.42482
哔哩哔哩动态(包含emoji)	0.27722	1.90657	0.01244	0.18507	0.55960
微博转发(竖图)	0.28995	2.58835	1.33334	0.41583	3.61492
微博图集(超过9张)	0.29929	1.23342	1.01614	0.31669	0.93084
微博图集(3张)	0.32397	1.03428	2.73813	0.34359	1.17222
微博图集(2张)	0.33608	1.16900	4.88308	0.64458	2.21195
微博图集(4张)	0.41367	1.71300	2.34023	0.72816	2.45148
B站动态	0.52926	3.20048	0.00653	1.34777	3.51336
微博图集(9张)	1.20037	2.04335	10.98936	0.98579	3.08158

[codecov]

Codecov Report

❌ Patch coverage is 87.09677% with 4 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
.../nonebot_plugin_parser/parsers/youtube/__init__.py	33.33%	2 Missing ⚠️
src/nonebot_plugin_parser/matchers/__init__.py	66.66%	1 Missing ⚠️
src/nonebot_plugin_parser/parsers/base.py	87.50%	1 Missing ⚠️

Files with missing lines	Coverage Δ
src/nonebot_plugin_parser/download/__init__.py	98.01% <100.00%> (+0.06%)	⬆️
src/nonebot_plugin_parser/parsers/__init__.py	100.00% <100.00%> (ø)
src/nonebot_plugin_parser/parsers/tiktok.py	93.75% <100.00%> (ø)
src/nonebot_plugin_parser/renders/__init__.py	51.61% <100.00%> (+3.12%)	⬆️
src/nonebot_plugin_parser/utils.py	70.88% <100.00%> (+1.14%)	⬆️
src/nonebot_plugin_parser/matchers/__init__.py	51.08% <66.66%> (ø)
src/nonebot_plugin_parser/parsers/base.py	90.83% <87.50%> (+1.52%)	⬆️
.../nonebot_plugin_parser/parsers/youtube/__init__.py	48.57% <33.33%> (ø)

... and 2 files with indirect coverage changes