feat: add streamedTotalLocal and sumStreamedTotal utils

[Yerimahjr]

Summary

Adds streamedTotalLocal(stream, nowSec?) and sumStreamedTotal(streams, nowSec?) to src/utils.ts, the client-side counterparts of StreamsModule.streamedTotal(), mirroring the existing withdrawableLocal / sumWithdrawable pair.

Closes #796

Changes

• streamedTotalLocal: cumulative amount streamed from a StreamInfo snapshot, with the same endTime-then-pausedAt clamp order as withdrawableLocal. Unlike withdrawableLocal, withdrawn is not subtracted, so the value keeps counting up after withdrawals.
• sumStreamedTotal: sums streamedTotalLocal across streams.
• Exported from the package root and /utils; documented in docs/api.md and CHANGELOG.md.
• Tests in src/tests/utils.test.ts, including a consistency check that streamedTotalLocal(s) - withdrawn matches withdrawableLocal(s) so the two can't drift apart.

Design note: cancelled streams

StreamInfo has no cancellation timestamp, so the amount streamed up to a cancel can't be projected locally. A cancelled stream reports its withdrawn amount (a lower bound that never overstates) instead of continuing to accrue. withdrawableLocal returns 0 for cancelled streams, but 0 would drop already-streamed amounts from a "total streamed" display. Happy to change this if the contract's streamed_total behaves differently after cancellation.

Testing

• src/tests/utils.test.ts: 94 passing (19 new).
• tsc --noEmit clean; eslint on the changed files has no new findings.
• Unrelated pre-existing failures in factory.test.ts, governor.test.ts and relayer-stress.test.ts (8 tests) occur identically on a clean upstream/main.

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