proxy: remove dead code (#8847)

By marking everything possible as pub(crate), we find a few dead code
candidates.

proxy/src/error.rs

@@ -3,12 +3,12 @@ use std::{error::Error as StdError, fmt, io};
 use measured::FixedCardinalityLabel;
 
 /// Upcast (almost) any error into an opaque [`io::Error`].
-pub fn io_error(e: impl Into<Box<dyn StdError + Send + Sync>>) -> io::Error {
+pub(crate) fn io_error(e: impl Into<Box<dyn StdError + Send + Sync>>) -> io::Error {
     io::Error::new(io::ErrorKind::Other, e)
 }
 
 /// A small combinator for pluggable error logging.
-pub fn log_error<E: fmt::Display>(e: E) -> E {
+pub(crate) fn log_error<E: fmt::Display>(e: E) -> E {
     tracing::error!("{e}");
     e
 }
@@ -19,7 +19,7 @@ pub fn log_error<E: fmt::Display>(e: E) -> E {
 /// NOTE: This trait should not be implemented for [`anyhow::Error`], since it
 /// is way too convenient and tends to proliferate all across the codebase,
 /// ultimately leading to accidental leaks of sensitive data.
-pub trait UserFacingError: ReportableError {
+pub(crate) trait UserFacingError: ReportableError {
     /// Format the error for client, stripping all sensitive info.
     ///
     /// Although this might be a no-op for many types, it's highly
@@ -64,7 +64,7 @@ pub enum ErrorKind {
 }
 
 impl ErrorKind {
-    pub fn to_metric_label(&self) -> &'static str {
+    pub(crate) fn to_metric_label(self) -> &'static str {
         match self {
             ErrorKind::User => "user",
             ErrorKind::ClientDisconnect => "clientdisconnect",
@@ -78,7 +78,7 @@ impl ErrorKind {
     }
 }
 
-pub trait ReportableError: fmt::Display + Send + 'static {
+pub(crate) trait ReportableError: fmt::Display + Send + 'static {
     fn get_error_kind(&self) -> ErrorKind;
 }