chore: remove deprecated LoaderSplitter

[shentongmartin]

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• The description of this PR title is user-oriented and clear enough for others to understand.
• Attach the PR updating the user documentation if the current PR requires user awareness at the usage level. User docs repo

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[github-actions]

⚠️ Breaking API Changes Detected

This pull request contains breaking API changes that may affect compatibility:

uncompatible api changes found: 
github.com/cloudwego/eino/components
  Incompatible changes:
  - ComponentOfLoaderSplitter: removed

github.com/cloudwego/eino/components/document
  Incompatible changes:
  - GetImplSpecificOptions: removed
  - LoaderSplitter: removed
  - LoaderSplitterOption: removed
  - WrapImplSpecificOptFn: removed

github.com/cloudwego/eino/compose
  Incompatible changes:
  - (*ChainBranch).AddLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Chain[I, O]).AppendLoaderSplitter: removed
  - (*Parallel).AddLoaderSplitter: removed
  - (*graph).AddLoaderSplitterNode, method set of *Graph: removed
  - (*graph).AddLoaderSplitterNode, method set of Graph: removed
  - WithLoaderSplitterOption: removed

Required Actions:

1. Please review these changes carefully
2. Update the user documentation to reflect these API changes
3. Add a note in the changelog about these breaking changes

[github-actions]

📊 Coverage Report:

File coverage threshold (20%) satisfied:	PASS
Package coverage threshold (30%) satisfied:	PASS
Total coverage threshold (75%) satisfied:	PASS
Total test coverage: 83.1% (2961/3565)

[hi-pender]

LGTM