ci: add RUSTFLAGS environment variable to CI workflows

- Introduced RUSTFLAGS environment variable in Python, Rust, and WASM CI workflows to override target-cpu settings from .cargo/config.toml, ensuring consistent build configurations across different environments.

.github/workflows/ci-python.yml

@@ -28,6 +28,8 @@ jobs:
   typecheck:
     name: Type checking (mypy + pyright)
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
@@ -49,6 +51,8 @@ jobs:
   build-wheel:
     name: Build wheel (ubuntu / Python ${{ matrix.python-version }})
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     strategy:
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13"]

.github/workflows/ci-rust.yml

@@ -57,6 +57,8 @@ jobs:
   rust-lint:
     name: Rust fmt + clippy
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     steps:
       - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@v1
@@ -75,6 +77,8 @@ jobs:
   rust-core:
     name: Rust core (build + test)
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     steps:
       - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@v1
@@ -91,6 +95,8 @@ jobs:
     name: Rust coverage (tarpaulin)
     runs-on: ubuntu-latest
     continue-on-error: true
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     steps:
       - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@v1
@@ -114,6 +120,8 @@ jobs:
     name: Fuzz targets (short CI run)
     runs-on: ubuntu-latest
     continue-on-error: true
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     steps:
       - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@v1

.github/workflows/ci-wasm.yml

@@ -10,6 +10,8 @@ jobs:
   wasm:
     name: WASM (test + build + bench)
     runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: ""  # override target-cpu=native from .cargo/config.toml
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-node@v6