Add configuration management (Config/AsyncConfig)

[ggiesen]

Summary

Adds a configuration management layer to librouteros, reachable via api.config(),
for RouterOS 7.x. It is implemented entirely over the binary API -- no SSH/terminal
access is required -- and adds no runtime dependencies (stdlib difflib only).

Config (sync) and AsyncConfig (async) provide:

• export() -- read the running config. /export returns nothing when run directly
  over the API, so this exports to a temporary file and reads it back.
• apply() / validate() -- /import a .rsc script, or dry-run it (verbose +
  dry-run, RouterOS 7.16+). Errors surface as TrapError with line and column.
• compare() -- unified diff of running vs candidate (informational; the module-level
  compare() diffs two strings directly).
• backup_save() / backup_load().
• arm_rollback() / cancel_rollback() / rollback_pending() -- a device-side
  /system/scheduler + backup dead man's switch (commit-confirm style). Because the
  timer lives on the device it survives a lost session or a lock-out, with no safe-mode
  action limit.
• replace() -- /system reset-configuration run-after-reset (wipe + reboot into a
  new config).

Why

Configuration management on RouterOS has historically been considered impractical over
the API (no config replace, no commit/rollback, safe mode is terminal-only). On
RouterOS 7.x the API is actually sufficient: /export file=... followed by reading the
/file contents retrieves a full export, /file/add + /import applies a script
(with errors reported), and a scheduler-based backup restore provides a rollback net
that survives a lock-out without needing safe mode.

Design notes

• No diff engine. Applying a config needs no computed patch (/import runs the
  script's own actions). compare() is a plain textual diff for humans, not an
  executable patch, so it cannot silently misapply.
• RouterOS has no native non-reboot commit/rollback, so the rollback timer lives on the
  device (a one-shot /system/scheduler that restores a backup), not on the client --
  it fires even if the client process dies.
• replace() is destructive and has no automatic rollback (safe mode is ignored for
  resets, the run-after-reset script must finish within ~2 minutes); documented as such.

Testing

• Unit tests (tests/unit/test_config.py): argument construction for every RouterOS
  command, diff/normalization logic, orchestration + temp-file cleanup (mocked helpers),
  and the query-builder helpers.
• Integration tests (tests/integration/test_config.py): export round-trip, merge
  apply, dry-run validation, compare, and the arm/pending/cancel rollback lifecycle,
  both sync and async, gated to RouterOS 7.x.
• Verified end to end against a CHR 7.21.5 instance, including the replace() reboot.
• ruff check, ruff format --check and mypy are clean.

Sync/async parity is maintained throughout. Documentation added at docs/config.rst.

[luqasz]

Hi

Thx for PR. I will review it in few days. Please be patient.