fix(srt): ignore embedded bom markers in subtitle input

Summary:
- Strip BOM characters from normalized input to avoid malformed SRT cue indices
- Add fixture test coverage for an embedded-BOM SRT sample file
- Add edge-case test proving embedded BOM does not break cue parsing

Author: dioKaratzas

Sources/SubtitleKit/Utilities/SubtitleNormalizer.swift

@@ -15,8 +15,7 @@ enum SubtitleNormalizer {
     }
 
     static func stripByteOrderMark(_ text: String) -> String {
-        guard text.unicodeScalars.first == "\u{FEFF}" else { return text }
-        return String(text.unicodeScalars.dropFirst())
+        text.replacingOccurrences(of: "\u{FEFF}", with: "")
     }
 
     static func inferLineEnding(_ text: String) -> LineEnding {

Tests/SubtitleKitTests/FixtureBasedTests.swift

@@ -4,6 +4,16 @@ import Testing
 
 @Suite("Fixture Parsing")
 struct FixtureParsingTests {
+    @Test("Parses embedded BOM SRT fixture")
+    func parseEmbeddedBOMSRTFixture() throws(any Error) {
+        let content = try FixtureSupport.fixtureText(
+            "embedded-bom-srt-fixture",
+            ext: "srt"
+        )
+        let subtitle = try Subtitle.parse(content, options: .init(format: .srt))
+        #expect(!subtitle.cues.isEmpty)
+    }
+
     @Test("Parses real fixtures", arguments: FixtureSupport.fixtureFormatNames)
     func parseFixture(for formatName: String) throws(any Error) {
         let format = FixtureSupport.format(named: formatName)
@@ -56,6 +66,14 @@ struct EdgeCaseTests {
         #expect(output.contains("\r\n"))
     }
 
+    @Test("Handles embedded BOM inside SRT stream")
+    func embeddedBOMInSRTStream() throws(any Error) {
+        let input = "0\n00:00:00,000 --> 00:00:01,000\nLead in\n\n\u{FEFF}1\n00:00:01,500 --> 00:00:03,000\nHello\n"
+        let subtitle = try Subtitle.parse(input, options: .init(format: .srt))
+        #expect(subtitle.cues.count == 2)
+        #expect(subtitle.cues[1].startTime == 1500)
+    }
+
     @Test("Throws on malformed timestamp")
     func malformedTimestampThrows() {
         let broken = "1\n00:AB:00,500 --> 00:00:02,000\nHello\n"

Tests/SubtitleKitTests/Fixtures/embedded-bom-srt-fixture.srt

@@ -0,0 +1,11 @@
+0
+00:00:00,000 --> 00:00:01,500
+Synthetic fixture header
+
+1
+00:00:01,600 --> 00:00:03,000
+<i>Embedded BOM cue line.</i>
+
+2
+00:00:03,100 --> 00:00:04,500
+<i>Follow-up cue line.</i>