feat: run transaction hooks at boundaries and add configurable LTO flags

- execute transaction pre hooks at transaction start and post hooks at transaction end
- add batched hook execution with ordered "(n/total)" logging
- refactor install flows to plan package actions first, then run hooks around commits
- add `build.flags.ltoflags` and `build.flags.use_lto` (default: true)
- export `LTOFLAGS` and append LTO flags to `CFLAGS`, `CXXFLAGS`, and `LDFLAGS`
  unless `use_lto = false`
- make autotools CFLAGS expansion use the final computed CFLAGS value
- update spec parsing/appends, interactive TOML output, docs, and contrib build config
- bump project version to 0.8.0 and update `zip` to 8.2.0

src/builder/autotools.rs

@@ -32,9 +32,14 @@ pub fn build(
         flags.cc.clone()
     };
 
-    if export_compiler_flags && !flags.cflags.is_empty() {
-        // Expand shell command substitutions like $($CC -print-resource-dir)
-        let cflags_str = flags.cflags.join(" ");
+    if export_compiler_flags
+        && let Some(cflags_str) = env_vars
+            .iter()
+            .find(|(key, _)| key == "CFLAGS")
+            .map(|(_, value)| value.clone())
+        && !cflags_str.trim().is_empty()
+    {
+        // Expand shell command substitutions like $($CC -print-resource-dir).
         let expanded = expand_shell_commands(&cflags_str, &cc)?;
         crate::builder::set_env_var(&mut env_vars, "CFLAGS", expanded);
     }