Update Taiwan Ethernet phrase mapping to prefer 乙太網路 in s2twp/tw2sp

[Copilot]

The current Taiwan phrase mapping for Ethernet favored 乙太網, while expected user-facing terminology is 乙太網路. This PR updates dictionary mappings so s2twp outputs 乙太網路 and tw2sp correctly normalizes both 乙太網路 and 乙太網 back to 以太网.

• Dictionary updates (Taiwan phrases)

  • Updated data/dictionary/TWPhrases.txt to prioritize 乙太網路 for 以太網, while keeping 乙太網 as an alternate.
  • Updated data/dictionary/TWPhrasesRev.txt to add reverse mapping for 乙太網路 -> 以太網 and preserve symmetry.

• Behavior coverage in testcases

  • Added focused cases in test/testcases/testcases.json:
    • s2twp: 以太网 → 乙太網路
    • tw2sp: 乙太網路 乙太網 → 以太网 以太网

• Mapping change (example)

  # TWPhrases.txt
  以太網    乙太網路 乙太網
  
  # TWPhrasesRev.txt
  乙太網路  以太網
  乙太網    以太網
  

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