Preserve MsPASS time and state through ObsPy decorators

[wangyinz]

Fixes #864

Summary

• carry UTC/relative mode, shifts, live state, and coherent sample-grid state through ObsPy decorators
• isolate conversion and prevalidate ensemble result length/order before any copy-back
• preserve the established dead-input short circuit: dead atomic data and all-dead/dead ensembles return None without invoking the wrapped ObsPy callable
• retain conversion/copy-back for mixed ensembles while restoring every member's MsPASS state
• return the original ensemble identity on successful ensemble operations

Renewed scientific/API review

The first version deleted the four decorators' existing is_input_dead guards, forced dead copies live, and ran arbitrary ObsPy operations on data that MsPASS had explicitly marked unusable. That was unrelated to the copy-back defect and could change samples/metadata before merely restoring the dead flag. Commit e89f4332 restores the original zero-call dead/all-dead boundary while keeping the state, relative-time, and atomic ensemble copy-back fixes.

Verification

• focused state/short-circuit contract: 41 passed
• contract plus full decorators, signals, and converter regressions: 75 passed
• all four decorators are tested with positional and keyword dead inputs; wrapped call count is exactly zero and full state is unchanged
• Black 26.5.1, Python 3.12/3.13 py_compile, and git diff --check: passed

This PR intentionally remains draft pending human API/scientific review.

[codecov]

Codecov Report

❌ Patch coverage is 84.97653% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.43%. Comparing base (61b06b9) to head (e89f433).

Files with missing lines	Patch %	Lines
python/mspasspy/util/decorators.py	84.97%	32 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #987      +/-   ##
==========================================
+ Coverage   68.35%   68.43%   +0.08%     
==========================================
  Files         173      173              
  Lines       34397    34526     +129     
  Branches     2474     2474              
==========================================
+ Hits        23511    23629     +118     
- Misses      10002    10013      +11     
  Partials      884      884              

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