dialects: (memref_stream) make bounds in dialect index typed not IntAttr

[superlopuh]

I really should not have been lazy and done this from the start. It makes sense from a semantic point of view, since these are converted to loop bounds, which are index-valued already.

Note stacked PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.80%. Comparing base (02c9118) to head (185a889).

Additional details and impacted files

@@                      Coverage Diff                      @@
##           sasha/riscv/unpeel-matmul    #2810      +/-   ##
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- Coverage                      89.81%   89.80%   -0.02%     
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  Files                            396      396              
  Lines                          49010    48844     -166     
  Branches                        7503     7482      -21     
=============================================================
- Hits                           44020    43865     -155     
+ Misses                          3802     3796       -6     
+ Partials                        1188     1183       -5     

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