[Issue #1305] standardize file naming

[gengdy1545]

Summary

Standardize all .pxl file naming conventions to resolve Issue #1305
(file naming issues in FileWriterManager). This is a subtask of Issue #1288
([pixels-retina, pixels-index, cpp] create new file) and lays the naming
foundation required by the Storage GC file-grouping and rewrite mechanism.

Background

Each write path (Retina CDC, batch load, compaction) used its own ad-hoc naming
scheme, making it impossible for Storage GC to reliably extract virtualNodeId
(for grouping files to rewrite), file type (for GC eligibility), and hostName
(for routing to the correct Retina service).

Changes

• Add PixelsFileNameUtils: Establishes a unified .pxl file name format
  <hostName>_<timestamp>_<count>_<virtualNodeId>_<type>.pxl as the single
  source of truth. Provides builder methods for all write paths
  (buildRetinaFileName, buildOrderedFileName, buildCompactFileName,
  buildSingleFileName, buildCopyFileName) and parser methods
  (extractHostName, extractVirtualNodeId, extractFileType, isGcEligible).
• Add NetUtils: Consolidates scattered hostname resolution logic from
  multiple modules into a shared utility with a well-defined fallback chain.
• Refactor CompactExecutor: Groups input files by virtualNodeId before
  compaction to preserve the delete_ts monotonicity invariant required by
  Storage GC; skips copy-type and unrecognized-format files; fixes in-place
  mutation of numRowGroupInBlock/compactLayout.
• Update all write paths (FileWriterManager, IndexedPixelsConsumer,
  SimplePixelsConsumer) to use the unified naming API.
• Simplify RetinaUtils: Replace inline hostname extraction with
  PixelsFileNameUtils.extractHostName() and isGcEligible().

Breaking Change

Existing files with the old naming format are incompatible with the new parser.
Migration or fresh deployment is required before upgrading.

Closes #1305
Part of #1288

[AntiO2]

LGTM