fix(jobs): split fp.jobs by thickness + serial on SO confirm

The _fp_auto_create_job grouping key was (recipe, part, coating).
Lines that shared all three but differed in thickness (or serial)
silently collapsed into one fp.job — the second line's thickness/SN
was lost, and any downstream cert printed the first line's values
across both batches. Silent mis-attestation = compliance hole.

Extended the key tuple to (recipe, part, coating, thickness, serial).
Single-line SOs and same-(thickness, SN) multi-line SOs collapse
identically to before. Only lines that previously merged when they
shouldn't have now split into their own fp.jobs.

TDD via test_so_confirm_splits_by_thickness:
  - seeds the part with default_process_id so both lines hit the
    `if recipe:` branch (where the bug lived — the no_recipe branch
    already split correctly per line)
  - confirms 2 jobs after action_confirm with each carrying its
    own thickness via the linked SO line

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_jobs/__manifest__.py

@@ -3,7 +3,7 @@
 # License OPL-1 (Odoo Proprietary License v1.0)
 {
     'name': 'Fusion Plating — Native Jobs',
-    'version': '19.0.8.22.10',
+    'version': '19.0.8.23.0',
     'category': 'Manufacturing/Plating',
     'summary': 'Native plating job model — replaces mrp.production / mrp.workorder bridge.',
     'author': 'Nexa Systems Inc.',