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.

Cargo.lock

@@ -2186,7 +2186,7 @@ dependencies = [
 
 [[package]]
 name = "mhrv-rs"
-version = "1.2.5"
+version = "1.2.6"
 dependencies = [
  "base64 0.22.1",
  "bytes",