fix: CFI module — 11 issues from code review

Phase 1 (correctness):
- #1: rawValue changed from stored to computed property, eliminating stale cache risk
- #2: tokenSamples/textMarker unified to UTF-16 offsets, fixing emoji/CJK positioning
- #3: makeOffsetCFI now accepts optional contentPath parameter

Phase 2 (robustness):
- #4: Resolver uses fixed index access instead of last(where:) for manifest/spine steps
- #5: HTML comments and CDATA stripped before regex matching
- #6: Text assertion parser handles backslash escapes (\[ \] \)
- #7: Token matching uses prefix/suffix with length ratio constraints
- #8: makeOffsetRangeCFI validates startOffset <= endOffset

Phase 3 (code quality):
- #9: Shared internal nilIfEmpty extension in RDEPUBCFIUtilities.swift
- #10: RDEPUBCFIMap has markerByPath index dictionary for O(1) lookup
- #11: parseRange unified to use try (not try?) for parent parsing

Review fixes:
- Documented init(rawValue:) parameter is ignored (computed property)
- Fixed escape unescaping to handle \\ → \ correctly
- Lowered token minLength threshold from 4 to 2

Co-Authored-By: Claude <noreply@anthropic.com>

Sources/RDReaderView/EPUBCore/CFI/RDEPUBCFICompatibility.swift

@@ -0,0 +1,29 @@
+import Foundation
+
+public enum RDEPUBCFICompatibility {
+    public static func parseLossy(_ rawValue: String?) -> RDEPUBCFI? {
+        try? RDEPUBCFIParser.parse(rawValue)
+    }
+
+    public static func parseRangeLossy(_ rawValue: String?) -> RDEPUBCFIRange? {
+        if let parsed = try? RDEPUBCFIParser.parseRange(rawValue) {
+            return parsed
+        }
+
+        guard let rawValue,
+              !rawValue.isEmpty else {
+            return nil
+        }
+
+        let separators = ["..", "-"]
+        let separator = separators.first(where: { rawValue.contains($0) })
+        guard let separator else { return nil }
+        let parts = rawValue.components(separatedBy: separator)
+        guard parts.count == 2,
+              let start = parseLossy(parts[0]),
+              let end = parseLossy(parts[1]) else {
+            return nil
+        }
+        return RDEPUBCFIRange(parent: nil, start: start, end: end)
+    }
+}