v1.2.6: rust-cache bin pruning fix + PR #83 scan-sni

v1.2.4 and v1.2.5 both cut clean tags but CI failed downstream for
different self-hosted reasons:

- v1.2.4 failed on parallel apt-lock race (fixed)
- v1.2.5 failed with "TOML parse error at line 5 column 9" because
  rust-cache v2's default cache-bin=true prunes $CARGO_HOME/bin of
  any binary not installed via `cargo install`. `rustup` itself is
  installed by rustup-init, not cargo install, so it got flagged as
  "unknown" and deleted on cache save. Next job hits the cargo
  symlink that points at a missing rustup, which resolves somehow
  to a very old cargo that can't parse our Cargo.toml.

Fix:
- Set `cache-bin: "false"` on every Swatinem/rust-cache@v2 call.
  We still cache target/ + registry (the big win), just not bin/.
  Binaries are stable across runs on our self-hosted box anyway.
- Reinstalled rustup inside each per-runner CARGO_HOME on the server
  to recover from the broken state.

Also in this release:
- PR #83: new `mhrv-rs scan-sni` subcommand. Pulls Google's
  published IP ranges, does PTR lookups via dns.google on each IP,
  filters to Google-related hostnames, then TLS-probes each
  discovered SNI against the configured google_ip to see which ones
  bypass DPI. Useful for rebuilding a working SNI pool on a new ISP.
  Adds the `url` crate dep.

Same user-facing code as v1.2.4/v1.2.5 (PRs #78, #79, README Android
note) plus PR #83 and the CI fixes on top.

.github/workflows/release.yml

@@ -106,10 +106,19 @@ jobs:
       # `git clean -ffdx` wipes target/ between runs and every build is
       # cold. With it, warm builds are sub-minute even for the full
       # release profile.
+      #
+      # cache-bin: false is MANDATORY on our self-hosted runners. With
+      # the default (true), rust-cache aggressively prunes $CARGO_HOME/bin
+      # of binaries it didn't install via `cargo install`, including the
+      # `rustup` binary that cargo/rustc/etc. are symlinked to. The next
+      # job then hits "command not found" or a broken-symlink TOML parse
+      # error from a stale cargo. We want target/ + registry caching, NOT
+      # bin pruning. rustup is pre-installed on the runners anyway.
       - uses: Swatinem/rust-cache@v2
         if: matrix.mipsel_softfloat != true
         with:
           key: ${{ matrix.target }}
+          cache-bin: "false"
 
       # eframe needs a few system libs on Linux for window management, keyboard,
       # and OpenGL/X11/Wayland. Gated to GitHub-hosted runners only — the
@@ -343,9 +352,14 @@ jobs:
       # Cache cargo + target/ across Android release builds. Four cargo-ndk
       # release builds back-to-back with LTO is where the cold cost comes
       # from; rust-cache brings warm runs down to ~3–4 min from ~9 min cold.
+      # cache-bin: false — see the rationale on the matrix build job above.
+      # On top of that, `cargo-ndk` lives in /usr/local/bin/ on our runners
+      # (not $CARGO_HOME/bin), specifically so rust-cache's default bin
+      # pruning can't delete it.
       - uses: Swatinem/rust-cache@v2
         with:
           key: android-universal
+          cache-bin: "false"
           # cargo-ndk writes into `target/<android-triple>/release/`, all
           # four of which we want to cache.
           workspaces: |