V2

- add support for configurable icons and highlights in symbols configuration
- implement dynamic width calculation with percentage support
- improve highlight handling with namespace-based extmarks
- add devicons integration for file-like nodes
- update lsp command calls to use client:request syntax
- refactor preview and hover windows with markdown support
- normalize configuration options in setup function
- add tree guide line highlights with configurable highlight group
- fix buffer and window option handling with nvim_set_option_value

Reorganize the codebase for clearer separation of concerns:
- Move view-related modules into a `views` subdirectory
  (`view`, `data_provider`, `data_node`, `tree_item`, `writer`,
  `parser`, `mappings`, `explorer_node`).
- Consolidate jdtls enums and node data classes:
  - Add `java/enums.lua` aggregating `NodeKind`, `TypeKind`,
    `PackageRootKind`, `ContainerEntryKind`, nature/container
    constants.
  - Replace `nodeData.lua` with `node_data.lua`, and split the
    specialized subclasses into `package_root_node_data.lua`,
    `container_node_data.lua`.
  - Add `node_data_factory.lua` to wrap raw jdtls responses into
    the appropriate `NodeData` subclass by `kind`.
- Rename `lsp-command.lua` to `lsp_command.lua`; remove the old
  `IPackageRootNodeData.lua`/`ContainerEntryKind.lua` files.
- Delete `hieararchicalPackageNodeData.lua` in favor of the
  rewritten `hierarchical_package_node_data.lua`.
- Standardize identifiers to snake_case across the API and move
  the hierarchical-view toggle into the `hierarchical_view`
  config option (documented in README).
- Fix a typo in the project sorting/filter logic and drop a
  redundant `Folder` branch in `load_data`.

…ency containers

- Add `symbols.icons.ProjectKind` / `symbols.icons.ContainerKind` icon categories with `symbols.highlights` counterparts
- Distinguish jdtls-lsp icon use of PackageRoot nodes so sync status between vscode-java-dependency nodes marked by `entry_kind`/`container_path`
- Fall from `ProjectKind` / `AdditionalPath` styles to `NodeKind` icon font coding those mark