refactor(core): share process-tree kill helpers across tool crates (#853)

Five crates (tools, build, vcs, github, docker) each carried their own copy of killing a child and what it started, and only the tools installer killed the whole tree on Windows, so cancelling git, gh, docker or Maven/Gradle there left descendants running. ide-core now provides own_group, kill_tree and terminate_tree (process-group signals on Unix, taskkill /T /F on Windows) and the copies are removed. Unix behaviour is unchanged; the Windows path was not run locally.

Co-authored-by: bograh <[email protected]>

Cargo.lock

@@ -4080,7 +4080,6 @@ dependencies = [
  "dirs 6.0.0",
  "dunce",
  "ide-core",
- "libc",
  "serde",
  "serde_json",
  "specta",
@@ -4104,6 +4103,7 @@ version = "0.1.33"
 dependencies = [
  "dunce",
  "encoding_rs",
+ "libc",
  "serde",
  "serde_json",
  "specta",
@@ -4173,7 +4173,6 @@ name = "ide-docker"
 version = "0.1.33"
 dependencies = [
  "ide-core",
- "libc",
  "serde",
  "serde_json",
  "specta",
@@ -4200,7 +4199,6 @@ version = "0.1.33"
 dependencies = [
  "ide-core",
  "ide-vcs",
- "libc",
  "serde",
  "serde_json",
  "specta",