feat(fusion_accounting_reports): pure-Python services for date+account+totaling

Three service modules with no Odoo dependencies:
- date_periods: fiscal year/month/quarter bounds + comparison derivation
- account_hierarchy: parent-child tree walker with type filtering
- totaling: move-line aggregation primitives

18 unit tests covering edge cases (December rollover, Feb 29, fiscal-
year-before-start, balance check tolerance).

Made-with: Cursor

fusion_accounting_reports/services/totaling.py

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+"""Move-line aggregation primitives for report totaling.
+
+Pure-Python helpers - callers pass dicts with debit/credit/balance/currency keys,
+no Odoo recordsets needed. Keeps the math testable without an ORM."""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class TotalLine:
+    debit: float = 0.0
+    credit: float = 0.0
+    balance: float = 0.0
+    debit_currency: float = 0.0
+    credit_currency: float = 0.0
+    balance_currency: float = 0.0
+    line_count: int = 0
+
+
+def aggregate(move_lines: list[dict]) -> TotalLine:
+    """Aggregate a list of move-line dicts into a TotalLine.
+
+    Each dict must have: debit, credit, balance (signed). Optional:
+    debit_currency, credit_currency, balance_currency."""
+    out = TotalLine()
+    for ml in move_lines:
+        out.debit += ml.get('debit', 0.0)
+        out.credit += ml.get('credit', 0.0)
+        out.balance += ml.get('balance', 0.0)
+        out.debit_currency += ml.get('debit_currency', 0.0)
+        out.credit_currency += ml.get('credit_currency', 0.0)
+        out.balance_currency += ml.get('balance_currency', 0.0)
+        out.line_count += 1
+    return out
+
+
+def aggregate_per_account(move_lines: list[dict]) -> dict[int, TotalLine]:
+    """Group + aggregate by account_id. Returns {account_id: TotalLine}."""
+    grouped: dict[int, list[dict]] = {}
+    for ml in move_lines:
+        acct = ml['account_id']
+        grouped.setdefault(acct, []).append(ml)
+    return {acct: aggregate(lines) for acct, lines in grouped.items()}
+
+
+def is_balanced(move_lines: list[dict], *, tolerance: float = 0.005) -> bool:
+    """True if total debits == total credits (within tolerance for rounding)."""
+    agg = aggregate(move_lines)
+    return abs(agg.debit - agg.credit) <= tolerance