BENCH: remove triple run of mmread/mmwrite benchmark, limit sizes

This fixes a problem on CircleCI. Closes scipygh-22574

This also reduced the runtime of the `io_mm` benchmarks by 10x,
it was super slow for no good reason because the benchmarks were
run 3 times, 2x with fast-matrix-market and 1x with the old pure
Python implementation. This looked like a left-over from the PR
that switched to fast-matrix-market, demonstrating that `io.mmread`
and `io.mmwrite` are the fast version and `io._mmio` is way slower.
There is no need to keep running that.

[skip actions] [skip cirrus]

Author: rgommers

benchmarks/benchmarks/io_mm.py

@@ -46,16 +46,20 @@ class MemUsage(Benchmark):
     def params(self):
         return [
             list(self._get_size().keys()),
-            ['scipy.io', 'scipy.io._mmio', 'scipy.io._fast_matrix_market'],
+            ['scipy.io'],
             ['dense', 'coo']  # + ['csr']
         ]
 
     def _get_size(self):
         size = {
             '1M': int(1e6),
             '10M': int(10e6),
-            '100M': int(100e6),
-            '300M': int(300e6),
+            '25M': int(10e6),
+            # Note: the below sizes should work locally but cause issues on CircleCI
+            #       it fails to allocate memory even though there is easily enough
+            #       available (see gh-22574).
+            #'100M': int(100e6),
+            #'300M': int(300e6),
             # '500M': int(500e6),
             # '1000M': int(1000e6),
         }