meson: fail early when no LAPACK/OpenBLAS/BLAS dependency is available

[RyanHaotianPang]

Motivation

• Fix a build-system bug where Meson could silently continue when dependency('lapack', required: false) was not found, producing an extension with unresolved LAPACK symbols such as dgeev_ that only surface at import/runtime.
• Ensure configuration fails early with a clear message if no LAPACK provider is available so a broken extension cannot be produced.

Description

• Update meson.build to probe lapack first, fall back to openblas, then blas, and call error(...) if none are found, while preserving the existing lapack_dep usage for linking.
• Add a one-line note to README.md indicating that building from source requires a LAPACK provider (LAPACK, OpenBLAS, or BLAS).
• Keep the change minimal and localized to meson.build and a single README clarification.
• Commit message: meson: require LAPACK provider at configure time and PR title matches this change.

Testing

• Verified the patch was applied and the repository diff with git diff -- meson.build README.md and git show succeeded.
• Attempted to run Meson configure with meson --version && meson setup builddir_test --wipe, but Meson is not installed in this environment so configure could not be executed (configuration/run failed).
• No automated test-suite changes were made; suggest adding a lightweight CI check that runs meson setup on Linux with BLAS/LAPACK packages to prevent regressions in future.