hecatron 0.3.0

• An installer: curl -fsSL …/install.sh | sh installs the latest
  release into ~/.hecatron and adds it to bash, zsh and fish startup files;
  sourced from a clone, it also sets up the current shell. Rerun to update.
  It first installs what hecatron needs if it's missing: the Command Line
  Tools on macOS, and git, Python 3 and perl on Linux (apt, dnf or zypper).
• Downloads retry transient failures (timeouts, dropped connections,
  429 and 5xx answers, stalled transfers) in installers, hooks, apt and the
  installer's git operations; a 404 isn't retried.
• A smoke test for every language: each builds and runs a small program
  with the freshly installed toolchain, and checks its output.
• Groovy, Scala and Kotlin install their own compilers (Groovy 5.1.3,
  Scala 3.3.8 LTS, Kotlin 2.4.21), not only the JDK.
• Default hooks for every language. A conventional project needs no hook
  files: each language's test, lint, build and clean commands are chosen from
  the build files present (#36).
• New languages: JavaScript, Objective-C and Haxe, for 54 in all (#36).
• Toolchain versions for Python, Go, Rust, Node.js and Java: a pinned
  default (Python 3.15.1, Go 1.27.3, Rust 1.99.1, Node.js 24.22.1 LTS,
  Temurin JDK 25.0.5 LTS), or the version a component's own pin file asks
  for, installed side by side (#19, #27, #28). A component on the default
  accepts any installed version on the default's release line (#31). The JDK
  is Temurin rather than the distribution's OpenJDK 17, and Node.js comes from
  nodejs.org rather than NodeSource.
• hct init finds real layouts: directory aliases such as dotnet/,
  javascript/ and lib/py, a directory per language where one template
  doesn't fit, and examples, tests and vendored code skipped (#33, #34, #35,
  #37).
• Generated Dockerfiles install every version the components use (#30).
• hct self-test runs ShellCheck and the unit tests; hecatron checks at
  startup for bash 3.2+ and Python 3.9+, and no longer asks for bash 4 (#38).
• Hecatron or ad hoc?, a ten-language
  library maintained with hecatron and without it (#15).
• Fixes for macOS (Python, Mojo, D, Lua, Pharo, Go) and Debian
  (PowerShell) from the first full coverage run (#32), Ruby gems with native
  extensions (#25), and Wren on arm64 (#21).