fix(coverage): stream coverage data json to disk

[gultekinmakif]

• Because this PR includes a bug fix, relevant tests have been included.

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Summary

This PR addresses a bug:

Large --coverage runs fail with RangeError: Invalid string length when the serialized coverage map exceeds Node's JSON.stringify / JSON.parse string-length ceiling.

Fix

Both saveData and loadData now use writeJsonFileAsStream / readJsonFileAsStream instead of their non-streaming counterparts. The rationale comment mirrors build-system.ts:1035.

Tests

Introducing any regression tests would not make any sense, so I tested the behaviour change locally.

I ran a small Node script that builds a Record<string, number> of 5,000,000 coverage-tag-shaped entries (~520 MB serialized, same order of magnitude as the failure on the linked issue).

The script confirms that this PR is able to stream large files, while the main branch fails.

Changeset

patch on hardhat.

Notes

• Other writeJsonFile call sites that might exhibit similar behavior on sufficiently large inputs:
  • build-system.ts:1027
  • gas-analytics-manager.ts:109
  • gas-analytics-manager.ts:151
  • snapshot-cheatcodes.ts:224
• Closes Coverage fails to write huge json when tests completed #8071

[claude]

Claude Code Review

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[changeset-bot]

🦋 Changeset detected

Latest commit: b9cbaab

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
hardhat	Patch

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[alcuadrado]

Can you provide a reproduction of the bug with the latest version first? We already did some things related to this recently, so the bug may not be present.

[alcuadrado]

I ran a small Node script that builds a Record<string, number> of 5,000,000 coverage-tag-shaped entries (~520 MB serialized, same order of magnitude as the failure on the linked issue).

This would be equivalent to having 5M solidity statements in a single project

[gultekinmakif]

@alcuadrado I've spun up a small script to replicate the issue across 3.1.6, 3.1.12, and latest versions: hh-8071-poc.

POC concludes that #8213 already addressed both issues that resurface.
I think #8071 can also be marked as fixed.
Closing this PR.

[alcuadrado]

Thanks a lot for the follow up investigation, @gultekinmakif! Appreciate it :)