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

contrib/depot.d/build.toml

@@ -10,6 +10,10 @@ cflags += ["-pipe"]
 # Default LDFLAGS
 ldflags = ["-Wl,-O1"]
 
+# Default LTOFLAGS and automatic injection into CFLAGS/CXXFLAGS/LDFLAGS.
+ltoflags = ["-flto=auto"]
+use_lto = true
+
 # CARCH short name (can be overridden per-package)
 carch = "x86_64"