refactor(L2): tighten BaseTime NatSpec and tests

[0x00101010]

Summary

• Complete IBaseTime NatSpec: correct the BaseTime_InvalidTimestampMillisPart description (above 800 or not a multiple of 200), enumerate setTimestampMillisPart reverts in execution order, add @param/@return, and document that timestampMs() combines the current seconds with the previous block's millisecond component until the block's tx[1] update executes.
• Drop the named return from BaseTime.timestampMs.
• Run BaseTime tests against the genesis-installed predeploy via CommonTest (adds baseTime to Setup), fuzz by default, order reverts before happy paths, pin that the depositor check precedes the value check, and drop the initial-value test already covered by L2Genesis.t.sol.

Runtime bytecode is unchanged. The node pins BaseTime's runtime code hash, so this PR is deliberately bytecode-neutral: keccak256(deployedBytecode) stays 0x9c4c8a497a69d0b8f2ba67be0bee7a1373186055978c3be6ec3068e0ec27f32a. version stays 1.0.0; only semver-lock.json's sourceCodeHash and the ABI snapshot's output name (timestampMs_ → unnamed) change. No selector, error, or storage change.

Test plan

• just test (full suite) passes
• forge fmt --check, just snapshots-check-no-build
• cast keccak $(jq -r '.deployedBytecode.object' forge-artifacts/BaseTime.sol/BaseTime.json) == 0x9c4c…f32a

Companion change in base-std (read-only IBaseTime + StdPredeploys.BASE_TIME): base/base-std#238.

[cb-heimdall]

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[amiecorso]

nice!

[cb-heimdall]

Review Error for amiecorso @ 2026-10-08 22:37:17 UTC
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