build: upgrade to go 1.19 (#25726)

This changes the CI / release builds to use the latest Go version. It also
upgrades golangci-lint to a newer version compatible with Go 1.19.

In Go 1.19, godoc has gained official support for links and lists. The
syntax for code blocks in doc comments has changed and now requires a
leading tab character. gofmt adapts comments to the new syntax
automatically, so there are a lot of comment re-formatting changes in this
PR. We need to apply the new format in order to pass the CI lint stage with
Go 1.19.

With the linter upgrade, I have decided to disable 'gosec' - it produces
too many false-positive warnings. The 'deadcode' and 'varcheck' linters
have also been removed because golangci-lint warns about them being
unmaintained. 'unused' provides similar coverage and we already have it
enabled, so we don't lose much with this change.

p2p/nat/nat.go

@@ -53,12 +53,12 @@ type Interface interface {
 // The following formats are currently accepted.
 // Note that mechanism names are not case-sensitive.
 //
-//     "" or "none"         return nil
-//     "extip:77.12.33.4"   will assume the local machine is reachable on the given IP
-//     "any"                uses the first auto-detected mechanism
-//     "upnp"               uses the Universal Plug and Play protocol
-//     "pmp"                uses NAT-PMP with an auto-detected gateway address
-//     "pmp:192.168.0.1"    uses NAT-PMP with the given gateway address
+//	"" or "none"         return nil
+//	"extip:77.12.33.4"   will assume the local machine is reachable on the given IP
+//	"any"                uses the first auto-detected mechanism
+//	"upnp"               uses the Universal Plug and Play protocol
+//	"pmp"                uses NAT-PMP with an auto-detected gateway address
+//	"pmp:192.168.0.1"    uses NAT-PMP with the given gateway address
 func Parse(spec string) (Interface, error) {
 	var (
 		parts = strings.SplitN(spec, ":", 2)