detect IP-based throttling (download test phase)

[rcd27]

Summary

blockcheckw status currently classifies domains as Available / SNI Blocked / IP Blocked / DNS
Failed.
It misses a critical case: IP-based throttling — where TCP connects, TLS handshake passes,
but data transfer is throttled to near-zero after ~16-19KB.

Real-world example: Discord (March 2026). 4 out of 5 Cloudflare IPs throttled,
TLS handshake succeeds, first ~19KB arrive, then speed drops to 0.
Users see "infinite loading" and think the bypass tool is broken.

Problem

Current status flow:
DNS → TCP SYN → TLS + HTTP HEAD → verdict

HTTP HEAD returns 200 → status reports "Available". But the site doesn't actually work
because bulk data transfer is throttled.

Proposed Solution

Add download test phase after HTTP HEAD succeeds:

DNS → TCP SYN → TLS + HTTP HEAD → Download ~100KB → verdict

New verdict: IpThrottled

Detection logic:

• Request a known-large resource (or the page itself with full body)
• If < 50KB downloaded in 10 seconds → IpThrottled
• If ≥ 50KB at reasonable speed → Available

http_test_data() already exists in network/http_client.rs with streaming body support.
interpret_data_transfer_result() already detects DpiDataLimit in 10-25KB range.
The infrastructure is there — needs to be wired into cmd/status.rs.

Output Example

discord.com
DNS: ✓ resolves (162.159.136.232, ...)
TCP SYN: ✓ connects
TLS: ✓ handshake OK
Download: ✗ THROTTLED — 19KB/10s (expected >50KB)

Verdict:   IP-THROTTLED

ℹ Traffic to this resource's IP addresses is throttled by the ISP.
  DPI bypass (zapret2) won't help — throttling is IP-based.
  Solution: VPN or proxy (Podkop, AmneziaWG, VLESS).

Per-IP breakdown (nice to have)

Discord has 5 IPs, only 1 works. Would be useful to test each resolved IP separately
and show which are throttled:

162.159.128.233:  ✗ throttled (19KB/10s)
162.159.135.232:  ✗ throttled (17KB/10s)
162.159.136.232:  ✓ OK (15MB/0.6s)
162.159.137.232:  ✗ throttled (19KB/10s)
162.159.138.232:  ✗ throttled (17KB/10s)

JSON output

Add to StatusDomainResult:

{
  "domain": "discord.com",
  "block_type": "ip_throttled",
  "speed_kbps": 1.2,
  "ips_tested": [
    {"ip": "162.159.128.233", "speed_kbps": 1.2, "throttled": true},
    {"ip": "162.159.136.232", "speed_kbps": 24000.0, "throttled": false}
  ]
}