no-std Step 8 — Set `ndarray` dependency to `default-features = false`

[Mec-iS]

Part of #413 — feat: no-std feature flag for embedded/edge targets

Task

The ndarray dependency (0.17, optional, ndarray-bindings feature) currently inherits its default features, which include std. ndarray 0.17 natively supports no_std + alloc.

Change Required

In Cargo.toml, update the ndarray dep entry:

# Before
ndarray = { version = "0.17", optional = true }

# After
ndarray = { version = "0.17", optional = true, default-features = false, features = ["std"] }

Then, in the no_std path (i.e. when std feature is disabled), the ndarray-bindings feature should not pull ndarray/std:

[features]
ndarray-bindings = ["dep:ndarray"]    # drop ndarray/std from this line
std = ["ndarray/std", ...]            # let std feature re-enable it

Acceptance

• cargo check --no-default-features --features ndarray-bindings compiles without pulling std from ndarray
• cargo build --features "default,ndarray-bindings" (with std) compiles and all ndarray-backed tests pass
• No std-only ndarray API (e.g. ndarray::Array::from_file) is used anywhere in smartcore's ndarray-bindings code path

Estimated effort

~30 min. One Cargo.toml line change + verification that no std-only ndarray surface is used.

Dependencies

Independent — can be done in parallel with Steps 1, 3, 4, 7.