Tests: add forward proxy and CONNECT tunnel coverage

[anchmelev]

• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added tests that prove my fix is effective or that my feature works.
• If applicable, I have checked that any relevant tests pass after adding my changes.
• I have updated any relevant documentation (README.md and/or CHANGELOG.md).

This adds companion test coverage for OSS forward proxy support and CONNECT tunneling.

The new tests cover HTTP/1.1, HTTP/2, and HTTP/3 behavior for both CONNECT tunnels and ordinary HTTP forward proxying.

Added tests

CONNECT tunnel coverage

• tunnel.t
• h2_tunnel.t
• h3_tunnel.t

These tests cover:

• successful HTTP/1.1 CONNECT tunnel establishment
• bidirectional relay
• preread and pipelined client data
• large payload transfer
• tunnel_allow_upstream
• retry vs no-retry behavior
• resolver and no-resolver cases
• unix socket tunnel upstreams
• tunnel_bind / tunnel_bind_dynamic
• HTTP/2 CONNECT
• HTTP/3 CONNECT
• rejection when tunnel support is not configured
• missing :authority handling for H2/H3 CONNECT

Forward proxy coverage

• forward_proxy.t
• forward_proxy_conf.t
• forward_proxy_ipv6.t
• h3_forward_proxy.t

These tests cover:

• HTTP/1.1 absolute-form GET/HEAD/POST
• rewrite to origin-form upstream requests
• Host reconstruction from target authority
• rejection of origin-form requests in forward proxy mode
• rejection of https://... targets without CONNECT
• rejection of CONNECT when only forward_proxy on; is configured
• hostname targets resolved via resolver
• no-resolver failure paths
• IPv6 targets
• HTTP/2 forward proxy behavior
• HTTP/3 forward proxy behavior
• configuration-time validation for forward_proxy and proxy_pass
• inheritance and override cases for forward_proxy on/off

Harness update

lib/Test/Nginx.pm is updated to recognize the new http_tunnel module in feature checks.

Validation

This test set was run together with the corresponding nginx implementation changes, along with existing regression coverage for proxy and H2/H3 request body handling.

Companion implementation PR: nginx/nginx#1217

This PR adds companion tests for the OSS forward proxy support introduced in nginx/nginx#1217.

[anchmelev]

I have hereby read the F5 CLA and agree to its terms