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/paginatedreader/PaginatedReader.kt

@@ -158,6 +158,7 @@ import coil.compose.AsyncImage
 import coil.imageLoader
 import coil.request.ImageRequest.Builder
 import com.aryan.reader.R
+import com.aryan.reader.ReaderTexture
 import com.aryan.reader.countWords
 import com.aryan.reader.epub.EpubBook
 import com.aryan.reader.epubreader.HighlightColor
@@ -529,7 +530,7 @@ fun PaginatedReaderScreen(
     val context = LocalContext.current
     val textureBitmap = remember(activeTextureId) {
         activeTextureId?.let { id ->
-            com.aryan.reader.epubreader.ReaderTexture.entries.find { it.id == id }?.resId?.let { resId ->
+            ReaderTexture.entries.find { it.id == id }?.resId?.let { resId ->
                 androidx.compose.ui.graphics.ImageBitmap.imageResource(context.resources, resId)
             }
         }