solver: align equilibrium/rocket/shock iteration behavior with legacy CEA2 and expand CI coverage

[markleader]

Summary

This PR updates the equilibrium, rocket, and shock solvers to better match legacy CEA2 iteration behavior and edge-case handling, with a focus on singular recovery, condensed-species activation/order, frozen-flow scheduling, and convergence criteria. It also updates CI to build/test across a broader compiler/OS matrix and publish build artifacts for tagged releases.

Changes

• source/equilibrium.f90
  • Added/used active-element counting and element swap/restore helpers for singular-recovery paths.
  • Tightened condensed-species activation/deactivation/replacement flow and active-order handling.
  • Updated iteration controls and convergence checks (including max_iterations, esize, pi denominator guards, and absolute-value mole checks) to better track legacy behavior.
  • Applied condensed validity checks in TP solves and fixed related index/phase transitions.
• source/rocket.f90
  • Updated frozen/throat/area-ratio iteration tolerances and convergence logic to legacy-style criteria.
  • Added frozen schedule gating for invalid pi/p and Ae/At points and ensured omitted points do not consume output indices.
  • Added frozen condensed temperature-range guard band checks and explicit non-convergence handling.
  • Fixed FAC/throat initialization and pressure-update details used by frozen expansions.
• source/shock.f90
  • Updated convergence thresholding and first-iteration temperature-cap behavior for incident/reflected paths.
  • Seeded incident equilibrium from reactant composition to match legacy initialization behavior.
  • Corrected reflected-frozen enthalpy/cp evaluation path to use incident frozen composition (gas-only where appropriate).
  • Added early exits when prior shock states fail (zeroed temperature/pressure markers).
• .github/workflows/basic_build.yml
  • Reworked build matrix to explicit labeled jobs across Linux/macOS/Windows (including arm64/aarch64 where available).
  • Added Windows MSYS2 gfortran setup path and explicit compiler selection via FC.
  • Enabled C bindings in CI builds and added verification/upload of CLI + C ABI artifacts.
  • Added tag-triggered release-artifact job with checksum generation.
• CHANGELOG.md
  • Added draft changelog notes for the upcoming patch release.

Testing

• Not run locally (changes were prepared for CI validation via the expanded GitHub Actions matrix and existing project test targets).

Compatibility / Numerical behavior

• No expected changes to numerical results
• Expected changes (explain and provide validation)
  • Expected numerical differences in some edge cases due to solver convergence/initialization/gating changes intended to match legacy CEA2 behavior more closely (especially condensed-phase, frozen-flow scheduling, and shock iteration paths).
  • Validation plan: compare representative equilibrium/rocket/shock outputs against legacy CEA2 baselines and review CI matrix results for cross-compiler consistency.