Pdf reader improvments (#113)

* Improve PDF rendering quality and performance.

- Set `FilterQuality.High` when drawing base bitmaps and high-res tiles in `PdfPageComposable`.
- Implement `inSampleSize` calculation in `UniversalDocument` to optimize memory usage during region decoding.
- Enhance bitmap drawing quality by adding `ANTI_ALIAS_FLAG` and `DITHER_FLAG` to the paint configuration.

* Implement custom reader themes for PDF viewer.

This change integrates the `ReaderThemePanel` and theme management logic into the PDF viewer, allowing users to apply preset or custom themes. Previously, the PDF viewer only supported a simple dark mode toggle.

Specific changes:
- Moved `ReaderTheme`, `ReaderTexture`, and theme-related utility functions from `EpubReaderScreen.kt` to `Common.kt` to allow sharing between EPUB and PDF readers.
- Updated `PdfPageComposable` to use `activeTheme` instead of `isDarkMode`, implementing a `ColorMatrix` to apply custom background and text colors to PDF pages.
- Replaced the dark mode toggle in `PdfViewerScreen` with a theme selection button that opens `ReaderThemePanel`.
- Introduced `PdfBuiltInThemes` to provide PDF-specific theme presets.

* Reset page transformation on constraint changes and refine tile rendering logic.

- Reset scale to 1.0 and offset to zero in `PdfPageComposable` when constraints change.
- Update `UniversalDocument` to use floating-point precision for source rectangle calculations and `RectF` for destination mapping to improve rendering accuracy.

* Improve eraser hit detection and visual thickness settings in PDF reader.

app/src/main/java/com/aryan/reader/pdf/PdfVerticalReader.kt

@@ -111,7 +111,6 @@ import com.aryan.reader.SearchResult
 import com.aryan.reader.pdf.data.PdfAnnotation
 import com.aryan.reader.pdf.data.PdfTextBox
 import com.aryan.reader.pdf.data.VirtualPage
-import io.legere.pdfiumandroid.suspend.PdfDocumentKt
 import kotlinx.coroutines.FlowPreview
 import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.delay
@@ -177,7 +176,7 @@ private data class DividerLayout(val y: Float, val width: Float, val height: Flo
 internal fun PdfVerticalReader(
     state: VerticalPdfReaderState,
     pdfDocument: StableHolder<ReaderDocument>,
-    isDarkMode: Boolean,
+    activeTheme: com.aryan.reader.ReaderTheme,
     totalPages: Int,
     modifier: Modifier = Modifier,
     virtualPages: List<VirtualPage> = emptyList(),
@@ -243,6 +242,7 @@ internal fun PdfVerticalReader(
         }
     }
     var globalEraserPosition by remember { mutableStateOf<Offset?>(null) }
+    val isDarkMode = activeTheme.isDark || activeTheme.id == "reverse"
     BoxWithConstraints(modifier = modifier.fillMaxSize(), contentAlignment = Alignment.TopStart) {
         val imeInsets = WindowInsets.ime
         val density = LocalDensity.current
@@ -1497,7 +1497,7 @@ internal fun PdfVerticalReader(
                                     pageIndex = page.index,
                                     virtualPage = virtualPage,
                                     totalPages = totalPages,
-                                    isDarkMode = isDarkMode,
+                                    activeTheme = activeTheme,
                                     externalScale = highResScale,
                                     onScaleChanged = {},
                                     showAllTextHighlights = showAllTextHighlights,