Update to SCTK 0.18.0

The main highlight is the move to calloop to handle all the requests
which makes it possible to remove all the active polling and clean the
data reading/writing, as well as accepting arbitrary long payloads.

This update also fixes the CI for the repository by moving it to github
actions, sets the minimum rust version, and edition to 2021.

Fixes #46.
Fixes #44.
Fixes #34.

rustfmt.toml

@@ -1,4 +1,16 @@
-use_small_heuristics = "Max"
+format_code_in_doc_comments = true
+match_block_trailing_comma = true
+condense_wildcard_suffixes = true
 use_field_init_shorthand = true
+normalize_doc_attributes = true
+overflow_delimited_expr = true
+imports_granularity = "Module"
+use_small_heuristics = "Max"
+normalize_comments = true
+reorder_impl_items = true
+use_try_shorthand = true
 newline_style = "Unix"
-edition = "2018"
+format_strings = true
+wrap_comments = true
+comment_width = 80
+edition = "2021"