Replace Travis with ALPS-style GitHub Actions

[egull]

Summary

• replace Travis CI with a GitHub Actions workflow modeled on ALPS 3.0
• test GCC 11/13/15, Clang 15/19, and AppleClang on macOS arm64
• add LAPACK, ASan/UBSan, strict, and ALPS-compatible-flags variants
• build and cache ALPSCore as the current backend
• update the README badge, dependencies, and test instructions

Local validation

• workflow YAML parses successfully
• 42 unit tests pass
• complete fast regression suite passes

[Copilot]

Copilot review overview

🟡 Changes recommended

Unresolved moderate issues remain in CI cache invalidation, grid consistency, and regression comparison handling.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

• macOS cache key omits toolchain and dependency versions · New
• Seed invariant ignores selected sets and cases · New

What changed in this PR

Replaces Travis CI with ALPS-style GitHub Actions and improves cross-platform testing, regression validation, and documentation.

Changes:

• Adds Linux/macOS compiler, sanitizer, LAPACK, and ALPSCore CI variants.
• Updates bootstrap regression checks, provenance, and tests.
• Updates CMake configuration, README instructions, and default-model normalization.

File	Summary	Review notes
test/​regression/​test_generate.py	Adds bootstrap validation tests.	No final comment.
test/​regression/​REFERENCE_CHANGES.md	Documents reference regeneration.	No final comment.
test/​regression/​PROVENANCE.md	Documents bootstrap provenance.	No final comment.
test/​regression/​compare.py	Adds bootstrap output and seed validation.	Moderate issues: apply tolerance to booterr, respect selection filters, and guard missing datasets.
src/​maxent.cpp	Adds the required formatting header.	No final comment.
src/​default_model.cpp	Updates symmetric-grid normalization.	Moderate issue: centralize grid-point calculations across mappings.
README.md	Updates badge, dependencies, and test instructions.	No final comment.
CMakeLists.txt	Updates Eigen checks and warning handling.	No final comment.
ALPS3_MIGRATION_PLAN.md	Records migration progress.	No final comment.
.travis.yml	Removes Travis configuration.	No final comment.
.github/​workflows/​build.yml	Adds the GitHub Actions CI matrix and ALPSCore caching.	Moderate issues: include complete compiler/toolchain and dependency versions in cache keys.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Unresolved moderate findings affect CI reliability, grid consistency, and malformed bootstrap handling.

Review effort: Lite
Findings: None

Resolved since last review (2)

• Seed invariant ignores selected sets and cases
• macOS cache key omits toolchain and dependency versions

Previously missed (1)

In code that hasn't changed since last review

Cache key omits exact compiler toolchain identity

.github/​workflows/​build.yml:79

The Linux dependency cache key distinguishes only the compiler family and major version. ALPSCore records the exact downstream compiler ID/version and Maxent rejects an install built with a different compiler identity (the migration plan documents this stale-compiler failure at ALPS3_MIGRATION_PLAN.md:704), so a GCC/Clang patch update can restore an incompatible cached ALPSCore and fail during find_package(ALPSCore). Include the full compiler version/toolchain identity in the key, or invalidate this cache whenever the runner toolchain changes.

[egull]

Addressed the latest Copilot finding in 67d8bcf. Linux ALPSCore/Boost cache keys now include a fingerprint of the exact C++ compiler build and the installed HDF5, Eigen, and Open MPI package versions, preventing reuse across runner toolchain or dependency updates.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Resolve the ALPSCore pinning, Eigen version-check, and malformed bootstrap-data handling issues.

Review effort: Lite
Findings: None