fix(commons): handle missing MAC addresses

[imbajin]

Purpose of the PR

VPN and tunnel interfaces can have an IP address without a hardware address. Previously MAC discovery threw a NullPointerException and left an empty cache, hiding usable interfaces on the next call.

Main Changes

• Skip unavailable hardware addresses when collecting MACs, while keeping direct lookups as explicit failures.
• Publish the MAC cache only after the complete collection succeeds, so lookup errors remain retryable.

Normal MAC encoding, IP enumeration, public signatures and PD IP/MAC identity selection remain unchanged.

Verifying these changes

• Trivial rework / code cleanup without any test coverage. (No Need)
• Already covered by existing tests.
• Need tests and can be verified as follows:

Added real-JDK loopback and mixed-interface/deduplication controls, plus a deterministic retry regression. Commons and RPC consumer suites, full reactor compilation, formatting and a redacted real-interface before/after control pass.

Does this PR potentially affect the following parts?

• Dependencies
• Modify configurations
• The public API
• Other affects
• Nope

Documentation Status

• Doc - TODO: required documentation is pending; complete it before merging.
• Doc - Done: documentation is included here or linked below.
• Doc - No Need: this is an internal helper correction with no new configuration or website behavior.

PD REST identity-pairing acceptance remains a separate follow-up.

Summary by CodeRabbit

• Bug 修复
  • 改进 MAC 地址获取的稳定性：遇到网卡未提供硬件地址、地址重复或查询失败时，不再因空值引发意外异常。
  • 无可用 MAC 地址时返回空结果；地址查询失败后再次调用可重新尝试获取。

Paired org PR: hugegraph#307

Conceptual overview

MAC 批量收集跳过缺失硬件地址，仅完整成功后发布缓存，单地址查询仍明确失败。

Conceptual illustration; not test or release-acceptance evidence.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.00%. Comparing base (62faab7) to head (661e8b3).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3335      +/-   ##
============================================
+ Coverage     52.80%   55.00%   +2.20%     
+ Complexity     6059      436    -5623     
============================================
  Files           762      511     -251     
  Lines         67674    48665   -19009     
  Branches       9189     6984    -2205     
============================================
- Hits          35736    26770    -8966     
+ Misses        28394    19214    -9180     
+ Partials       3544     2681     -863     

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[imbajin]

Addressed the outside-diff diagnostic comment. The required missing-hardware-address check now preserves its specific exception message through the existing PD message-only reporting path. Optional MAC aggregation still skips missing addresses and retains the original cache and retry behavior.

The existing loopback regression verifies the diagnosis, and the final Commons suite passes on the tested platform. The native interface tests retain their explicit platform assumptions; adding a production injection hook would expand this focused fix. All three independent reviewers checked the published two-file delta. New-head CI remains open.