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

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "depot"
-version = "0.7.0"
+version = "0.8.0"
 edition = "2024"
 
 [lints.rust]
@@ -27,7 +27,7 @@ toml = "0.9.8"
 url = "2.5.8"
 walkdir = "2.5.0"
 xz2 = "0.1.7"
-zip = "8.1.0"
+zip = "8.2.0"
 zstd = { version = "0.13.3", features = ["zstdmt"] }
 inquire = "0.9.4"
 md5 = "0.8.0"