docs: functional checks, the behaviour a release exists for

[0xrajath]

Motivation

docs/testing.md mapped safe-sim's structural checklist to LatticeTest helpers but said nothing about the other half of a release's tests: the behaviour the release exists for, driven end to end through the live proxies after the change.

Modifications

• docs/testing.md: a Functional checks section — what to cover (the changed behaviour, one happy path that must keep working, failure paths the change moved), how to do it on a fork (prank the role holders, write the inputs the flow needs; nothing reaches the chain under lattice test or lattice run), everything from Env, when a release may skip it.

Result

A release writer knows a Functional.t.sol suite is expected beside the structural ones, and how to write one that runs unchanged against the sandbox and against mainnet.

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Note

Low Risk
Documentation-only change to testing guidance; no runtime or contract behavior is modified.

Overview
Adds a Functional checks section to docs/testing.md that sits alongside the existing structural upgrade checklist and describes what release tests must prove about behaviour, not just proxy mechanics.

It expects a Functional.t.sol suite (via a verify step in test mode after live bytecode / post-deploy checks) to cover the changed flow end-to-end through live proxies, at least one regression happy path, and any failure paths the change moved. It documents how to run those tests on a fork—prank role holders, seed inputs, use Env for addresses—why unit tests are not a substitute, and when a release may skip the suite.

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