Validate string model deserialization and derived length bounds

[isPANN]

Summary

• Reuse constructor validation when loading ClosestString, GroupingBySwapping, LongestCommonSubsequence, ShortestCommonSupersequence, ShortestCommonSuperstring, and StringToStringCorrection.
• Recompute the three derived maximum-length fields from input strings instead of trusting serialized values.
• Share construction checks and length calculations with create specifications while retaining their existing input requirements.
• Preserve public constructor signatures, serialized output fields, and solver/reduction interfaces. Twelve files, based directly on main.

Verification

• All nine new regressions fail on main, covering invalid inputs and corrupted length bounds/search dimensions.
• Full workspace all-feature tests: 6,487 passed; 2 existing ignored.
• Miscellaneous model coverage run: 1,079 passed; changed-line coverage 98.54% across 205 lines.
• Workspace all-target all-feature Clippy with warnings denied, formatting, and diff whitespace checks passed.

[codecov]

Codecov Report

❌ Patch coverage is 98.53659% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.93%. Comparing base (7dd5fcd) to head (6fec366).

Files with missing lines	Patch %	Lines
src/models/misc/closest_string.rs	96.15%	1 Missing ⚠️
src/models/misc/grouping_by_swapping.rs	95.45%	1 Missing ⚠️
src/models/misc/string_to_string_correction.rs	96.29%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #1165    +/-   ##
========================================
  Coverage   95.93%   95.93%            
========================================
  Files        1074     1074            
  Lines      132106   132201    +95     
========================================
+ Hits       126730   126833   +103     
+ Misses       5376     5368     -8     

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[isPANN]

Consolidated into #1166 as string and scheduling input validation. Combined all-feature workspace tests and Clippy pass.