Missing TLS overhead in byte statistics when using HTTPS upstream proxy

[bliuchak]

When using an HTTPS upstream proxy, connection statistics (trgRxBytes/trgTxBytes) only count application-layer bytes and miss TLS overhead.

This affects both handlers:

• forward.ts (HTTP requests via HTTPS upstream)
• chain.ts (CONNECT tunneling via HTTPS upstream)

Expected behavior: Byte counts should include all TCP bytes by accessing the _parent socket of TLS connection.

npm run test test/https_upstream_tls_overhead.js
...
  2 passing (1s)
  2 failing

  1) forward.ts TLS overhead with HTTPS upstream
       should demonstrate missing TLS overhead with HTTPS upstream proxy:

      counted trgRxBytes 171 not equal to actual upstream count 2300
      + expected - actual

      -171
      +2300

      at Context.<anonymous> (test/https_upstream_tls_overhead.js:230:44)

  2) chain.ts TLS overhead with HTTPS upstream
       should demonstrate missing TLS overhead with HTTPS upstream proxy (chain handler):

      counted trgRxBytes 2339 not equal to actual upstream count 4512
      + expected - actual

      -2339
      +4512

      at Context.<anonymous> (test/https_upstream_tls_overhead.js:495:44)