fix: Fix asset prefix double-prefixing and sprite name stripping

[gnarhard]

Description

Bug 1: Image loading double-prefixes paths

loadAtlasDataImages applied assetsPrefix (designed for Flame.assets, prefix assets/) to Flame.images (prefix assets/images/), causing paths like assets/images/images/packs/textures.png. The image path should be passed directly to img.load() without the assets prefix, as it was in 5.0.5.

Bug 2: _parseRegion strips trailing digits from sprite names

The regex (_?)(\d+)$ in _parseRegion strips trailing digits from all sprite names, assuming they're animation frame indices. This breaks any sprite whose name naturally contains trailing digits (e.g. drohne2 → drohne, cu3 → cu, crystal2 → crystal). In 5.0.5, the name was always kept as-is and the index only came from the explicit index: field in the atlas.

Fix 1: Double-prefixed image paths in loadAtlasDataImages

assetsPrefix (default 'images') was applied to both Flame.assets (prefix assets/) and Flame.images (prefix assets/images/), causing paths like assets/images/images/packs/texture.png.

The else branch in loadAtlasDataImages prepended assetsPrefix to texturePath before passing it to images.load(). Since Flame.images already adds assets/images/, this created a double prefix. The
subsequent stripping logic was fragile — it relied on AssetsCache.prefix aligning with Images.prefix, which silently failed in non-standard configurations.

Changes:

• lib/src/texture_packer_parser.dart — loadAtlasDataImages:
  • Removed assetsPrefix and assets parameters (no longer needed for image loading)
  • Removed the assetsPrefix prefix application block
  • Replaced the toRelative/relativePrefix stripping logic with a simpler approach that directly checks for overlap with img.prefix (both full and partial), independent of AssetsCache configuration
  • Changed texturePath from var to final (no longer reassigned)
• lib/src/texture_packer_atlas.dart — loadAtlas:
  • Removed the now-unnecessary assetsPrefix and assets arguments from the loadAtlasDataImages call
• test/atlas_path_resolution_test.dart:
  • Added test: assetsPrefix is not applied to image paths loaded via Images
  • Added test: subdirectory image paths are not double-prefixed

Fix 2: Aggressive digit stripping from sprite names in _parseRegion

The regex r'(_?)(\d+)$' unconditionally stripped trailing digits from all sprite names and treated them as animation frame indices. This broke any sprite whose name naturally ends in digits (e.g. drohne2 →
drohne, cu3 → cu, vine1 → vine, corruption_sack-1 → corruption_sack-).

v5.1.0 added name-based index extraction that can't distinguish between animation indices (walk_01) and names that end in digits (drohne2). In v5.0.5, the index only came from the explicit index: field in the
atlas file.

Changes:

• lib/src/texture_packer_parser.dart — _parseRegion:
  • Removed the regex-based index extraction block (the indexMatch logic and nameBeforeIndex/extractedIndex variables)
  • finalIndex now only uses the explicit index: field from the atlas, defaulting to -1
  • Region name is the original name from the atlas (with file extension stripped), never modified
• test/naming_index_test.dart:
  • Updated all tests to expect names preserved as-is (image1, image_01, etc.) with index -1
  • Renamed test for explicit index: field to verify it still works
• test/separated_parsing_test.dart:
  • Updated to expect sprite1 preserved as name (not stripped to sprite)
  • Updated getAnimation test to use explicit index: fields in atlas content
• test/atlas_path_resolution_test.dart:
  • Updated existing test to expect preserved names (knight_walk_01, not knight_walk)
  • Added new test verifying explicit index: field still works correctly

Tests

• All 60 existing + new tests pass
• Dart analyzer reports no errors
• New/legacy/whitelist format tests unaffected (they use explicit index: fields)
• Image path tests verify no double-prefixing with default and custom assetsPrefix
• Naming tests verify sprite names with trailing digits are preserved
• Animation test updated to use explicit index: fields (the supported mechanism)

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

[spydon]

Looks sensible to me.
Do you want to have a look @s1r1m1r1, since you made these changes?
So that we don't bounce back and forth,

[s1r1m1r1]

I tested this fix,
but when loading from a package, the PNG file for the atlas doesn't load correctly.

Perhaps I should add some fixes for loading images for the atlas from the package.

[s1r1m1r1]

If there are too many changes, it's possible to
revert to just one index pattern: image1, image2, image3, image4, etc.
Revert changes only for package integration.