Add CAUSAL padding for 1D convolution.

[copybara-service]

Add CAUSAL padding for 1D convolution.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[codecov-commenter]

Codecov Report

Merging #2141 (c5708be) into main (c22f7d4) will increase coverage by 0.01%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##             main    #2141      +/-   ##
==========================================
+ Coverage   75.78%   75.79%   +0.01%     
==========================================
  Files          61       61              
  Lines        5302     5309       +7     
==========================================
+ Hits         4018     4024       +6     
- Misses       1284     1285       +1     

Impacted Files	Coverage Δ
flax/linen/linear.py	97.45% <85.71%> (-0.31%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c22f7d4...c5708be. Read the comment docs.