Add post_func_skip_list to control execution of post functions

[ZLI-afk]

In respond to required function associated with recent discussion topic #641 and #642

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 83.65%. Comparing base (a5ddff2) to head (f8d7389).

❗ Current head f8d7389 differs from pull request most recent head 01b43cb. Consider uploading reports for the commit 01b43cb to get more accurate results

Files	Patch %	Lines
dpdata/system.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            devel     #644      +/-   ##
==========================================
- Coverage   83.67%   83.65%   -0.02%     
==========================================
  Files          80       80              
  Lines        7006     7011       +5     
==========================================
+ Hits         5862     5865       +3     
- Misses       1144     1146       +2     

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[njzjz-bot]

Requesting changes because constructing an empty System and loading it later raises AttributeError before any post function can run. The branch must initialize this state before both constructor early returns, then be rebased and covered by chained-loading tests.

Process note: the Codex usage allowance is about to reset, so I am spending the remaining token budget now on this review.

Coding agent: Codex
Codex version: codex-cli 0.144.6
Model: gpt-5.6-sol
Reasoning effort: xhigh

[njzjz-bot]

[P1] Initialize the skip list before either early return

System() returns at file_name is None without defining post_func_skip_list. A later System().from_fmt(...) reaches the post-function branch and raises AttributeError, which I reproduced on this head. Move this initialization above both the data and file_name early-return blocks, and add a chained empty-constructor loading regression test. A complete GitHub suggestion cannot be attached to only these added lines because the fix must move them above unchanged context.