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

README.md

@@ -85,6 +85,10 @@ runtime = ["libc"]
 optional = ["bash-completion"]
 ```
 
+LTO controls are available via `build.flags`:
+- `ltoflags`: exported as `LTOFLAGS`
+- `use_lto`: defaults to `true`; when enabled, `ltoflags` are appended to `CFLAGS`, `CXXFLAGS`, and `LDFLAGS`
+
 ## Configuration
 
 Depot can be configured via `/etc/depot.d/` (or relative to the rootfs).