Add QCEW CSV module, ECEC breakdown, response caching + typed errors

Item 1 — QCEW county/industry detail:
- new bls_client/qcew.py: thin client over the QCEW Open Data CSV service
  (area/industry/size slices; no API key, no quota), with filter_rows helper
- covers the county/industry detail the timeseries API can't reach

Item 2 — ECEC benefit breakdown:
- new series.ecec() builder from the authoritative cm.estimate decode table
- real helpers: wages, total benefits, paid leave, supplemental pay,
  health insurance, retirement & savings, legally required + ecec_dashboard()
- FIX: ecec_total_benefits was CMU1036... (education/health industries only);
  correct all-civilian total benefits is CMU1030000000000D

Item 3 — caching + typed errors:
- bls_client/cache.py FileCache (on-disk, TTL); BLSClient(cache=True),
  queries_used counter (cache hits don't spend quota)
- bls_client/errors.py: BLSError / BLSQuotaError / BLSRequestError; quota
  exhaustion now raises a clear BLSQuotaError instead of a generic RuntimeError

Tests: 119 offline (+24) incl. ECEC goldens, QCEW fixture parse, cache/quota
behavior; live smoke extended to ECEC + QCEW. Helper sweep: 96/96 live.
README: caching/QCEW usage, updated coverage + limitations.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

bls_client/queries/wages.py

@@ -2,7 +2,7 @@
 Pre-built wage and compensation series IDs — OES, ECI, ECEC, CPS earnings.
 """
 
-from ..series import oes_national, eci
+from ..series import oes_national, eci, ecec
 
 # ---------------------------------------------------------------------------
 # OES — Occupational Employment & Wage Statistics
@@ -89,19 +89,58 @@ def eci_dashboard() -> dict:
 # ---------------------------------------------------------------------------
 # ECEC — Employer Costs for Employee Compensation
 # ---------------------------------------------------------------------------
-def ecec_total_compensation() -> str:
-    """ECEC — civilian workers, total compensation cost per hour worked."""
-    return "CMU1010000000000D"
+def ecec_total_compensation(owner: str = "civilian") -> str:
+    """ECEC — total compensation cost per hour worked."""
+    return ecec("total_compensation", owner)
 
 
-def ecec_total_benefits() -> str:
-    """ECEC — civilian workers, total benefits cost per hour worked."""
-    return "CMU1036000000000D"
+def ecec_wages_and_salaries(owner: str = "civilian") -> str:
+    """ECEC — wages and salaries cost per hour worked."""
+    return ecec("wages_and_salaries", owner)
 
-# Note: ECEC benefit subcomponents (health insurance, retirement & savings, etc.)
-# are encoded as specific benefit-subcell codes in the series ID (suffix stays "D").
-# Look them up against the ECEC component list before adding helpers — do not
-# fabricate them with a letter suffix (the old "...H"/"...R" forms were invalid).
+
+def ecec_total_benefits(owner: str = "civilian") -> str:
+    """ECEC — total benefits cost per hour worked."""
+    return ecec("total_benefits", owner)
+
+
+def ecec_paid_leave(owner: str = "civilian") -> str:
+    """ECEC — paid leave cost per hour worked (vacation, holiday, sick, personal)."""
+    return ecec("paid_leave", owner)
+
+
+def ecec_supplemental_pay(owner: str = "civilian") -> str:
+    """ECEC — supplemental pay cost per hour worked (overtime, bonuses, shift diff)."""
+    return ecec("supplemental_pay", owner)
+
+
+def ecec_health_insurance(owner: str = "civilian") -> str:
+    """ECEC — health insurance cost per hour worked."""
+    return ecec("health_insurance", owner)
+
+
+def ecec_retirement(owner: str = "civilian") -> str:
+    """ECEC — retirement & savings cost per hour worked (defined benefit + contribution)."""
+    return ecec("retirement_and_savings", owner)
+
+
+def ecec_legally_required(owner: str = "civilian") -> str:
+    """ECEC — legally required benefits per hour (Social Security, Medicare, UI, workers' comp)."""
+    return ecec("legally_required", owner)
+
+
+def ecec_dashboard(owner: str = "civilian") -> dict:
+    """The compensation cost breakdown — what an hour of labor costs an employer."""
+    return {
+        "Total Compensation": ecec_total_compensation(owner),
+        "Wages & Salaries":   ecec_wages_and_salaries(owner),
+        "Total Benefits":     ecec_total_benefits(owner),
+        "Paid Leave":         ecec_paid_leave(owner),
+        "Supplemental Pay":   ecec_supplemental_pay(owner),
+        "Health Insurance":   ecec_health_insurance(owner),
+        "Retirement & Savings": ecec_retirement(owner),
+        "Legally Required":   ecec_legally_required(owner),
+    }
 
 
 # ---------------------------------------------------------------------------