Fix Gemling Frost Wall Ice Crystal life

[xiaoyaoyang]

Fixes #2385.

Description of the problem being solved:

Advanced Thaumaturgy exposes Frost Wall's additional quality stat, ice_crystal_maximum_life_+%, but that stat was not mapped to PoB's internal IceCrystalLife modifier. As a result, the additional Ice Crystal Life from quality was read from the skill data and then silently discarded during skill modifier merging.

This maps the stat as increased Ice Crystal Life and adds a system regression test covering a 20/20 Frost Wall with Advanced Thaumaturgy allocated.

Steps taken to verify a working solution:

• Added a regression test that compares Frost Wall Ice Crystal Life before and after allocating Advanced Thaumaturgy.
• The test asserts that 20% quality grants 400% increased Ice Crystal Life, resulting in five times the unmodified value.
• Focused Frost Wall Busted test: 1 success, 0 failures, 0 errors.
• Complete spec/System/TestSkills_spec.lua: 61 successes, 0 failures, 0 errors.
• Ran git diff --check; repository GitHub Actions will also provide the authoritative test matrix and ModCache validation after maintainer approval for this first-time fork contribution.

Link to a build that showcases this PR:

https://pobb.in/CI4hChFipObn

Before screenshot:

N/A — calculation data fix. The linked build reports approximately 30,908 Ice Crystal Life in PoB despite Advanced Thaumaturgy.

After screenshot:

N/A — covered by the added system regression test.