[FEATURE] Add result caching for trim analyses

[camUrban]

Problem Statement

Trim analyses (analyze_steady_trim() and analyze_unsteady_trim()) run the solver many times across a parameter space. If a subsequent call expands the search bounds, all previously computed results are discarded and recomputed.

Location(s): pterasoftware/trim.py

Proposed Solution

Save intermediate results as JSON files so that subsequent calls with expanded bounds can skip previously computed parameter combinations and only evaluate new ones.