feat: plugin-declared parallel execution, switch to env_logger, update deps

Parallel execution (opt-in via MetaPlugin::parallel_safe):
- Add Send bound to MetaPlugin, parallel_safe() method (default false)
- Override to true in digest, tokens, exec, magic_file plugins
- MetaService: std::thread::scope for initialize_plugins and process_chunk
- Extract plugins via NullMetaPlugin sentinel + std::mem::replace (no unsafe)
- Panic tracking: join errors logged, NullMetaPlugin restored and finalized
- MetaPluginExec: Box<dyn Write> -> Box<dyn Write + Send>
- SendCookie wrapper for libmagic Cookie with unsafe impl Send

Logging (stderrlog -> env_logger):
- Custom format: [SSSSSS.mmm] LEVEL [module:] message (time-since-start ms)
- Default level: Warn (matches previous behavior)
- -v: Debug, -vv+: Trace, -q: off
- -vv+ shows module path

Maintenance:
- Bump deps: thiserror 2.0, config 0.15, dns-lookup 3.0, lz4_flex 0.12,
  ringbuf 0.4, rand 0.9, lazy_static 1.5, env_logger 0.11
- Update Cargo.lock (186 transitive packages)
- Clippy fixes: is_multiple_of, to_string_in_format_args, collapsible_if
- Fix double-counting bug in TokensMetaPlugin::update
- Fix schema description using plugin.description()

Co-Authored-By: opencode <noreply@opencode.ai>

src/meta_plugin/magic_file.rs

@@ -12,13 +12,36 @@ use crate::meta_plugin::{
     process_metadata_outputs,
 };
 
+/// Wrapper around `magic::Cookie` that is Send.
+///
+/// Libmagic cookies are thread-safe per-instance (separate cookies have
+/// independent state). The raw pointer `*mut magic_sys::magic_set` does not
+/// auto-derive Send, but concurrent access to distinct cookies is safe per
+/// the libmagic documentation.
+#[cfg(feature = "magic")]
+struct SendCookie(Cookie);
+
+#[cfg(feature = "magic")]
+// SAFETY: Each SendCookie owns a distinct libmagic instance. Libmagic
+// documents that separate cookies can be used from different threads
+// concurrently without synchronization.
+#[allow(unsafe_code)]
+unsafe impl Send for SendCookie {}
+
+#[cfg(feature = "magic")]
+impl std::fmt::Debug for SendCookie {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("SendCookie").finish()
+    }
+}
+
 #[cfg(feature = "magic")]
 #[derive(Debug)]
 pub struct MagicFileMetaPluginImpl {
     buffer: Vec<u8>,
     max_buffer_size: usize,
     is_finalized: bool,
-    cookie: Option<Cookie>,
+    cookie: Option<SendCookie>,
     base: BaseMetaPlugin,
 }
 
@@ -51,7 +74,8 @@ impl MagicFileMetaPluginImpl {
     }
 
     fn get_magic_result(&self, flags: CookieFlags) -> io::Result<String> {
-        if let Some(cookie) = &self.cookie {
+        if let Some(send_cookie) = &self.cookie {
+            let cookie = &send_cookie.0;
             cookie
                 .set_flags(flags)
                 .map_err(|e| io::Error::other(format!("Failed to set magic flags: {e}")))?;
@@ -125,7 +149,7 @@ impl MetaPlugin for MagicFileMetaPluginImpl {
             };
         }
 
-        self.cookie = Some(cookie);
+        self.cookie = Some(SendCookie(cookie));
 
         MetaPluginResponse {
             metadata: Vec::new(),
@@ -210,6 +234,10 @@ impl MetaPlugin for MagicFileMetaPluginImpl {
     ) -> anyhow::Result<&mut std::collections::HashMap<String, serde_yaml::Value>> {
         Ok(self.base.options_mut())
     }
+
+    fn parallel_safe(&self) -> bool {
+        true
+    }
 }
 
 #[cfg(feature = "magic")]
@@ -308,16 +336,15 @@ impl FallbackMagicFileMetaPlugin {
         }
 
         // Get human-readable file type via --brief
-        if let Some(file_type) = self.run_file_command(&["--brief"]) {
-            if !file_type.is_empty() {
-                if let Some(meta_data) = process_metadata_outputs(
-                    "file_type",
-                    serde_yaml::Value::String(file_type),
-                    self.base.outputs(),
-                ) {
-                    metadata.push(meta_data);
-                }
-            }
+        if let Some(file_type) = self.run_file_command(&["--brief"])
+            && !file_type.is_empty()
+            && let Some(meta_data) = process_metadata_outputs(
+                "file_type",
+                serde_yaml::Value::String(file_type),
+                self.base.outputs(),
+            )
+        {
+            metadata.push(meta_data);
         }
 
         metadata
@@ -415,6 +442,10 @@ impl MetaPlugin for FallbackMagicFileMetaPlugin {
     ) -> anyhow::Result<&mut std::collections::HashMap<String, serde_yaml::Value>> {
         Ok(self.base.options_mut())
     }
+
+    fn parallel_safe(&self) -> bool {
+        true
+    }
 }
 
 #[cfg(not(feature = "magic"))]