Simplify/modernize rrss2imap

[Riduidel]

Usage of tokio was a bad idea : code is way to much complex and should have been refactored prior to introducing async code. So let's do it now :

1. Remove tokio and all async code
2. Make code more map/reduce like
3. Use some concurrent collection system more able to help us

[Riduidel]

seems like I finally found a way to find big dpeendencies/functions : https://github.com/RazrFalcon/cargo-bloat

[Riduidel]

And result is quite terrible

 File  .text     Size Crate
 7.3%  12.8% 889.6KiB reqwest
 6.7%  11.9% 826.6KiB std
 6.2%  11.0% 764.9KiB tera
 2.4%   4.3% 295.8KiB clap
 2.3%   4.1% 281.8KiB rustls
 1.9%   3.3% 229.7KiB regex
 1.9%   3.3% 227.9KiB regex_syntax
 1.7%   3.0% 210.0KiB aho_corasick
 1.7%   3.0% 207.5KiB h2
 1.6%   2.9% 199.5KiB pest
 1.4%   2.5% 171.6KiB tokio
 1.2%   2.2% 152.8KiB hyper
 1.2%   2.1% 143.9KiB lol_html
 1.1%   1.9% 133.1KiB flexi_logger
 0.9%   1.5% 107.2KiB ring
 0.8%   1.5% 104.2KiB atom_syndication
 0.7%   1.3%  91.1KiB rss
 0.7%   1.2%  83.1KiB globset
 0.7%   1.2%  80.6KiB rrss2imap
 0.6%   1.1%  76.4KiB encoding_rs
10.6%  18.7%   1.3MiB And 119 more crates. Use -n N to show more.
56.5% 100.0%   6.8MiB .text section size, the file size is 12.0MiB

[Riduidel]

Wait, I have removed tera and reqwest, so the same now gives

 File  .text     Size Crate
 9.6%  14.8% 561.7KiB std
 4.7%   7.4% 278.8KiB clap
 4.7%   7.3% 275.6KiB rustls
 3.9%   6.0% 227.0KiB regex_syntax
 3.7%   5.7% 216.4KiB regex
 2.8%   4.4% 166.3KiB ureq
 2.5%   3.8% 144.9KiB lol_html
 2.4%   3.8% 143.5KiB aho_corasick
 2.3%   3.6% 136.0KiB flexi_logger
 1.8%   2.7% 104.0KiB atom_syndication
 1.7%   2.7% 100.5KiB rrss2imap
 1.5%   2.4%  89.3KiB rss
 1.3%   2.0%  76.4KiB encoding_rs
 1.3%   2.0%  74.5KiB imap_proto
 1.2%   1.9%  73.1KiB xml
 1.2%   1.8%  68.0KiB ring
 1.0%   1.5%  57.6KiB toml_edit
 0.8%   1.3%  49.8KiB treexml
 0.8%   1.3%  48.2KiB serde_json
 0.8%   1.2%  46.5KiB rustc_demangle
10.4%  16.2% 613.4KiB And 74 more crates. Use -n N to show more.
64.5% 100.0%   3.7MiB .text section size, the file size is 5.7MiB

[Riduidel]

Seems like things start to go in a good direction

File  .text     Size Crate
 9.8%  15.0% 565.8KiB std
 4.8%   7.4% 279.5KiB clap
 4.8%   7.3% 274.7KiB rustls
 3.9%   6.0% 227.1KiB regex_syntax
 3.7%   5.7% 215.9KiB regex
 2.9%   4.4% 167.2KiB ureq
 2.5%   3.8% 144.4KiB lol_html
 2.5%   3.8% 143.7KiB aho_corasick
 2.4%   3.7% 138.2KiB flexi_logger
 1.8%   2.8% 104.1KiB atom_syndication
 1.6%   2.5%  94.3KiB rrss2imap
 1.6%   2.5%  92.9KiB rss
 1.3%   2.0%  76.6KiB encoding_rs
 1.3%   2.0%  75.2KiB imap_proto
 1.3%   1.9%  72.5KiB xml
 1.2%   1.8%  68.0KiB ring
 1.1%   1.7%  65.7KiB mail_builder
 1.0%   1.5%  57.8KiB toml_edit
 0.9%   1.3%  49.4KiB treexml
 0.8%   1.3%  48.1KiB serde_json
 9.8%  15.0% 563.7KiB And 70 more crates. Use -n N to show more.
65.1% 100.0%   3.7MiB .text section size, the file size is 5.6MiB

Note: numbers above are a result of guesswork. They are not 100% correct and never will be.

[Riduidel]

Seems like #10 fixed also a good part of this

[Riduidel]

And currently, we have

 File  .text     Size Crate
14.7%  24.6% 629.4KiB std
 3.8%   6.3% 161.8KiB rrss2imap
 3.7%   6.3% 160.7KiB rustls
 3.5%   5.9% 150.9KiB clap
 3.2%   5.4% 137.8KiB regex
 2.5%   4.1% 106.1KiB aho_corasick
 2.4%   4.0% 102.1KiB regex_syntax
 1.9%   3.2%  81.4KiB lol_html
 1.7%   2.9%  73.8KiB ureq
 1.3%   2.3%  57.8KiB rss
 1.1%   1.8%  47.2KiB ring
 1.1%   1.8%  46.9KiB atom_syndication
 1.1%   1.8%  45.8KiB xml
 0.9%   1.5%  39.0KiB enum2$<encoding_rs
 0.9%   1.5%  37.4KiB imap_proto
 0.7%   1.2%  31.3KiB rustc_demangle
 0.7%   1.2%  31.1KiB chrono
 0.7%   1.2%  30.6KiB flexi_logger
 0.6%   1.0%  26.7KiB mail_builder
 0.6%   1.0%  24.4KiB selectors
 8.8%  14.8% 379.9KiB And 91 more crates. Use -n N to show more.
59.7% 100.0%   2.5MiB .text section size, the file size is 4.2MiB

[Riduidel]

In fact, I consider this fixed