https-dns-proxy: update to 2026.03.18-2

https-dns-proxy: update to 2026.03.18-2

Maintainer: me
Compile tested: x86_64, Dell EMC Edge620, OpenWrt 25.12.1
Run tested: x86_64, Dell EMC Edge620, OpenWrt 25.12.1

Description:
Fix nftables rule directory creation

  - Bump PKG_RELEASE to 2.

files/etc/init.d/https-dns-proxy:
  - Add 'mkdir -p' before writing nftables rules to ensure the parent
    directory exists. This fixes an issue where the directory might not
    exist on initial installation, causing errors.

tests/run_tests.sh:
  - Add comprehensive regression tests for notrack_nft.
  - Mock 'nft' to track invocations and control return codes for testing.
  - Patch 'NOTRACK_NFT_FILE' to a test-specific path for isolated testing.
  - Verify 'notrack_nft' correctly creates the parent directory if missing.
  - Test content of generated nftables snippet, idempotence, and removal.

Signed-off-by: Stan Grishin <redacted>