Refactor: Improve sqlx-core and sqlx-macros code quality #13

Job	Run time
clippy (sqlx-core-oldapi) • mysql • runtime-tokio-rustls	1m 28s
clippy (sqlx-rt-oldapi) • runtime-tokio-rustls	28s
clippy (sqlx-core-oldapi) • any • runtime-tokio-rustls	1m 20s
clippy (sqlx-core-oldapi) • mssql • runtime-tokio-rustls	1m 18s
clippy (sqlx-core-oldapi) • sqlite • runtime-tokio-rustls	1m 17s
clippy (sqlx-oldapi) • runtime-tokio-rustls,sqlite,macros	2m 24s
clippy (sqlx-rt-oldapi) • runtime-async-std-rustls	54s
clippy (sqlx-oldapi) • runtime-tokio-rustls,postgres,macros	2m 28s
clippy (sqlx-oldapi) • runtime-async-std-rustls,postgres,macros	2m 42s
clippy (sqlx-rt-oldapi) • runtime-async-std-native-tls	40s
clippy (sqlx-oldapi) • runtime-tokio-rustls,mysql,macros	2m 26s
clippy (sqlx-core-oldapi) • postgres • runtime-tokio-rustls	1m 16s
clippy (sqlx-rt-oldapi) • runtime-tokio-native-tls	33s
	19m 14s

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