Expand stateful streaming coverage to MACD ATR and BBANDS

[TDamiao]

Goal

Expand stateful/streaming coverage beyond SMA/EMA/RSI/VWAP session to match high-value batch indicators.

Why

Real-time first is a core differentiator; users need streaming variants of popular volatility/momentum indicators too.

Implementation prompt

Add stateful constructors for at least:

• MACD
• ATR
• BBANDS

API pattern:

• createX(config).next(value|candle)
• .reset() deterministic

Guarantee parity with batch outputs on overlapping non-null windows.

Scope

• Typed stateful interfaces and input validation
• Warmup semantics explicitly documented
• Efficient low-allocation update path

Acceptance criteria

• Streaming MACD/ATR/BBANDS exported and documented
• Parity tests vs batch with tolerance policy
• Reset behavior deterministic and tested
• README includes streaming examples for each added indicator

Test plan

• Unit tests for warmup, invalid input, and reset
• Golden/parity tests with batch references
• Optional compat checks where external streaming refs are available

[TDamiao]

Tracked by v0.4 master gate: #21.