feat(rewrite): instrument fn items inside macro_rules! definitions

add token-level scanner for fn patterns in macro_rules! templates.
injects piano_runtime::enter() guards with stringify!($name) for
metavar names and string literals for literal names. skips const fn,
unsafe fn, extern fn. handles generic parameters, brace/paren/bracket
delimiters, and fn inside impl blocks. activated when no --fn/--file/
--mod targets are specified via new instrument_macros parameter.

Author: rocketman-code

Cargo.lock

@@ -23,6 +23,7 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 ignore = "0.4"
 tempfile = "3"
+proc-macro2 = "1.0.106"
 
 [[bin]]
 name = "piano"

Cargo.toml

@@ -302,6 +302,7 @@ fn build_project(
     }
 
     // Rewrite each target file in staging.
+    let instrument_macros = specs.is_empty();
     let mut all_concurrency: Vec<(String, String)> = Vec::new();
     for target in &targets {
         let target_set: HashSet<String> = target.functions.iter().cloned().collect();
@@ -314,9 +315,11 @@ fn build_project(
             })?;
 
         let result =
-            instrument_source(&source, &target_set).map_err(|source| Error::ParseError {
-                path: staged_file.clone(),
-                source,
+            instrument_source(&source, &target_set, instrument_macros).map_err(|source| {
+                Error::ParseError {
+                    path: staged_file.clone(),
+                    source,
+                }
             })?;
 
         all_concurrency.extend(result.concurrency);