Make is_contiguous check common

[laggui]

Checklist

• Confirmed that run-checks all script has been executed.

Related Issues/PRs

Following this comment in #3077

Changes

Migrated is_contiguous to common (including minor fix).

Testing

Also added a unit test for shape [3, 1] and strides [1, 1] which would previously be marked as not contiguous.

[laggui]

Previously checked for prev_stride >= stride but equal adjacent strides are still valid.

See added test case for tensor shape [3, 1] with strides [1, 1], which would previously fail.

[laggui]

I also think the check could be simplified to

pub fn is_contiguous(shape: &[usize], strides: &[usize]) -> bool {
    if shape.is_empty() {
        return true;
    }

    let mut expected_stride = 1;

    for (&shape, &stride) in shape.iter().zip(strides).rev() {
        if shape == 1 {
            continue;
        }

        if stride != expected_stride {
            return false;
        }

        expected_stride *= shape;
    }

    true
}

But leaving this here as a note and not a required change.

[codecov]

Codecov Report

Attention: Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.14%. Comparing base (e096b0c) to head (f04fa77).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/burn-common/src/lib.rs	92.59%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3083      +/-   ##
==========================================
- Coverage   81.16%   81.14%   -0.02%     
==========================================
  Files         815      817       +2     
  Lines      117201   117314     +113     
==========================================
+ Hits        95121    95196      +75     
- Misses      22080    22118      +38     

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