Replace Line 49 proxy with direct M-CHIP sheet premium collections for CT, DE, MA, MI, NY

Follow-up from #8094.

## Problem

#8094 adds FY2024 cost-sharing offset data pulled from CMS Medicaid Financial Management Report CHIP Net Expenditures workbooks. For most states, the data is clean — it comes from the explicit "Premiums: Cost Sharing Offset" lines on the Separate CHIP sheets.

For five Medicaid-expansion / combination CHIP states — **CT, DE, MA, MI, NY** — the cost-sharing-offset lines are zero. These states' premium revenue appears on **Line 49 "Less Collection"** of the Separate CHIP sheet instead. We use Line 49 values as a proxy, but this line includes third-party liability (TPL) recoveries as well as premium receipts.

## Concern

The proxy introduces two errors:
1. **DE**: $140k reported vs schedule-expected $2-5M based on published premium tiers and enrollment. Clear under-reporting.
2. **NY**: FY2023 showed $99M (one-time reconciliation entry); FY2024 showed $9M (more plausible). Line 49 is noisy over time.
3. **MI**: $5.5M is within range of MIChild's $10/mo premium × ~84k enrollees × 12 = ~$10M but may include TPL.

## Proposed fix

Parse the CMS-21 M-CHIP sheets directly from the FY2024 workbook (and the M-CHIP 20% sheet, if applicable) to isolate premium-specific collection lines. The CMS-21 form Section 1A-D lines on M-CHIP sheets should carry pure premium collections separate from TPL recoveries.

File: `/tmp/FY 2024 FMR CHIP NET EXPENDITURES.xlsx` (or re-download from https://www.medicaid.gov/medicaid/financial-management/state-expenditure-reporting-for-medicaid-chip/expenditure-reports-mbescbes).

## Acceptance

- Replace Line 49 Less Collection proxies in `cost_sharing_offsets/*.yaml` with direct M-CHIP sheet premium collection values for CT, DE, MA, MI, NY.
- Expected CT ~$1.5-2M, DE ~$2-3M, MA ~$8-11M, MI ~$8-10M, NY ~$10-30M based on published premium schedules times rough enrollment.
- `per_capita_chip_gross` test updated if values shift substantially.