fix(ndt7): enumerate TCPInfo/BBRInfo fields to match legacy BigQuery order

[robertodauria]

Summary

De-embed tcp.LinuxTCPInfo/inetdiag.BBRInfo in the ndt7 model and enumerate their fields explicitly, ordered to reproduce the legacy ndt7 BigQuery table; reorder Measurement to [AppInfo, BBRInfo, TCPInfo, ConnectionInfo]. Adds NewTCPInfo/NewBBRInfo constructors; the measurer uses them.

bigquery.InferSchema previously emitted TCPInfo.ElapsedTime last (an artifact of embedding + a trailing field), so newly-autoloaded ndt7 tables diverged from the legacy parser table's nested field order. UNION ALL [BY NAME] coerces nested structs positionally, silently corrupting TCPInfo values (m-lab/etl-schema#195). Explicit enumeration makes the generated schema match the legacy table and enforces append-new-fields-at-the-end going forward.

Verification

• Regenerated ndt7 schema: full TCPInfo order is identical to measurement-lab.ndt.ndt7 (55/55 fields), and Measurement matches [AppInfo, BBRInfo, TCPInfo, ConnectionInfo].
• JSON wire format unchanged (identical field names) → no impact on emitted data or existing parsers.
• go build ./... and go vet ./ndt7/... pass.

Part of the fix for m-lab/etl-schema#195. Follow-ups (separate PRs): deploy the schema to GCS, then recreate the existing autojoin ndt7_raw tables.

---

This change is 

[coveralls]

Coverage Report for CI Build 26833216177

Coverage increased (+0.5%) to 76.444%

Details

• Coverage increased (+0.5%) from the base build.
• Patch coverage: 69 of 69 lines across 2 files are fully covered (100%).
• 2 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

2 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
ndt7/measurer/measurer.go	2	89.61%

---

Coverage Stats

Relevant Lines:	2390
Covered Lines:	1827
Line Coverage:	76.44%
Coverage Strength:	1.54 hits per line

---

💛 - Coveralls

[bassosimone]

🥳