feat(stateful): add streaming SMA/EMA APIs with parity and reset coverage

[TDamiao]

Summary

• add createSMA(period) and createEMA(period) to the stateful API
• keep warmup behavior deterministic and aligned with batch sma/ema
• keep reset() deterministic for repeated streaming runs
• export new constructors from root package entrypoint
• document websocket-like real-time usage in README
• extend golden tests with stateful parity and invalid-input validation

Validation

• npm.cmd run build
• node --test --test-concurrency=1 --test-isolation=none test/contracts.test.mjs
• node --test --test-concurrency=1 --test-isolation=none test/golden.test.mjs

Notes

• This PR is stacked on top of feat: standardize API typing and input variants for v0.3 gate #7 #9 (feat/issue-7-typing-ux) to keep review scope focused.
• In this sandbox, npm test with default isolation fails with spawn EPERM; commands above pass with --test-isolation=none.

Refs #2