fix: port main branch changes to channel subpackages after rebase

Port changes that were applied to the old pkg/channels/*.go files on main
to their new locations in channel subpackages:
- telegram: precompile regex, var transcribedText, GetModelName()
- discord: var transcribedText declaration
- onebot: resp.Body.Close(), "canceled" spelling, remove empty line
- slack: named return values in parseSlackChatID
- wecom: remove sendMarkdownMessage dead code
- whatsapp: resp.Body.Close() after Dial
- gateway/helpers: remove unused errors import

go.mod

@@ -19,6 +19,7 @@ require (
 	github.com/stretchr/testify v1.11.1
 	github.com/tencent-connect/botgo v0.2.1
 	golang.org/x/oauth2 v0.35.0
+	golang.org/x/time v0.14.0
 )
 
 require (
@@ -26,7 +27,6 @@ require (
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/spf13/pflag v1.0.10 // indirect
-	golang.org/x/time v0.14.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )