Feature: Support nominative reporter citations (5 U.S. (1 Cranch) 137)

[medelman17]

Problem

Citations with nominative (historical) reporters in parentheses are only partially parsed. The nominative reporter portion is silently ignored.

"5 U.S. (1 Cranch) 137"  → extracts "5 U.S. 137" only
                            nominative reporter "1 Cranch" is lost

These two citations should be recognized as semantically equal:

"5 U.S. 137"              → {volume: 5, reporter: "U.S.", page: 137}
"5 U.S. (1 Cranch) 137"   → {volume: 5, reporter: "U.S.", page: 137,
                              nominativeVolume: 1, nominativeReporter: "Cranch"}

Context

Early U.S. Supreme Court cases were published by private reporters (Dallas, Cranch, Wheaton, etc.). Modern citations include both the U.S. Reports reference and the historical reporter name in parentheses.

Expected Behavior

• Extract nominative reporter metadata when present
• Treat citations with and without nominative reporters as equal for hashing/comparison
• Store nominative info as optional fields: nominativeVolume, nominativeReporter

Upstream Reference

Python eyecite #154 — nominative reporters cause hash inequality.