This introduces a thread-local global memory allocator for each device
and uses it whenever there is an intermediate tensor needed which
requires zero-initialization.

To enable use `NVFUSER_ENABLE=reuse_zeroed_memory`. You can monitor the
allocator using `NVFUSER_DUMP=global_zeroed_memory`.

Before we enable this feature by default, we need to have high
confidence that every kernel using zero-initialized memory will always
clean up their semaphores. This is currently only the case for serial
grid reductions, as far as I know.

This enables the basic functionality of #1829. However, it does not
modify existing algorithms to clean up their memory. See
`NVFUSER_ENABLE=reuse_zeroed_memory NVFUSER_DUMP=global_zeroed_memory
build/nvfuser_tests --gtest_filter=SerialGridReductionTest.Scheduling`,
which succeeds when using serial grid reduction, but fails (in debug
mode) when using `gridReduce` (note that this test is updated to behave
differently in this PR):
```
# NVFUSER_ENABLE=reuse_zeroed_memory NVFUSER_DUMP=global_zeroed_memory build/nvfuser_tests --gtest_filter=SerialGridReductionTest.Scheduling                                                       
Running main() from /opt/pytorch/nvfuser/third_party/googletest/googletest/src/gtest_main.cc
Note: Google Test filter = SerialGridReductionTest.Scheduling
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from SerialGridReductionTest
[ RUN      ] SerialGridReductionTest.Scheduling
[global zeroed memory] Resizing arena to 512 bytes
[global zeroed memory] Allocating byte range: 0 to 512 bytes
[global zeroed memory] Resetting allocated bytes to 0
[global zeroed memory] Allocating byte range: 0 to 512 bytes
[global zeroed memory] Resetting allocated bytes to 0
[global zeroed memory] Resizing arena to 16384 bytes
[global zeroed memory] Allocating byte range: 0 to 16384 bytes
[global zeroed memory] Resetting allocated bytes to 0
[global zeroed memory] Allocating byte range: 0 to 16384 bytes
unknown file: Failure
C++ exception with description "nnz.equal(0) INTERNAL ASSERT FAILED at "/opt/pytorch/nvfuser/csrc/global_allocator.cpp":88, please report a bug with repro script to NVFuser at https://github.com/NVIDIA/Fuser/issues. Global memory arena was not properly zeroed. Found 2048 bytes that are not zero
Exception raised from checkZeroed at /opt/pytorch/nvfuser/csrc/global_allocator.cpp:88 (most recent call first):
frame #0: <unknown function> + 0x2fde9e (0x556cdb95de9e in build/nvfuser_tests)
frame #1: <unknown function> + 0x2fe0df (0x556cdb95e0df in build/nvfuser_tests)
frame #2: <unknown function> + 0x3f3720 (0x556cdba53720 in build/nvfuser_tests)
frame #3: <unknown function> + 0x3f33df (0x556cdba533df in build/nvfuser_tests)
frame #4: <unknown function> + 0x3f38ed (0x556cdba538ed in build/nvfuser_tests)
frame #5: <unknown function> + 0x315e67 (0x556cdb975e67 in build/nvfuser_tests)
frame #6: <unknown function> + 0x7c5780 (0x556cdbe25780 in build/nvfuser_tests)
frame #7: <unknown function> + 0x7c5877 (0x556cdbe25877 in build/nvfuser_tests)
frame #8: <unknown function> + 0x138f8cc (0x556cdc9ef8cc in build/nvfuser_tests)
frame #9: <unknown function> + 0x1457f0b (0x556cdcab7f0b in build/nvfuser_tests)
frame #10: <unknown function> + 0x14519fd (0x556cdcab19fd in build/nvfuser_tests)
frame #11: <unknown function> + 0x142de24 (0x556cdca8de24 in build/nvfuser_tests)
frame #12: <unknown function> + 0x142e93f (0x556cdca8e93f in build/nvfuser_tests)
frame #13: <unknown function> + 0x142f345 (0x556cdca8f345 in build/nvfuser_tests)
frame #14: <unknown function> + 0x143f86c (0x556cdca9f86c in build/nvfuser_tests)
frame #15: <unknown function> + 0x1458e98 (0x556cdcab8e98 in build/nvfuser_tests)
frame #16: <unknown function> + 0x1452ac7 (0x556cdcab2ac7 in build/nvfuser_tests)
frame #17: <unknown function> + 0x143de6d (0x556cdca9de6d in build/nvfuser_tests)
frame #18: <unknown function> + 0x1407ca0 (0x556cdca67ca0 in build/nvfuser_tests)
frame #19: <unknown function> + 0x1407c19 (0x556cdca67c19 in build/nvfuser_tests)
frame #20: <unknown function> + 0x29d90 (0x7f616c7d4d90 in /usr/lib/x86_64-linux-gnu/libc.so.6)
frame #21: __libc_start_main + 0x80 (0x7f616c7d4e40 in /usr/lib/x86_64-linux-gnu/libc.so.6)
frame #22: <unknown function> + 0x11e9d5 (0x556cdb77e9d5 in build/nvfuser_tests)
" thrown in the test body.

To reproduce: NVFUSER_TEST_RANDOM_SEED=1711120799 NVFUSER_TEST_ATEN_RANDOM_SEED=0 nvfuser_tests --gtest_filter='SerialGridReductionTest.Scheduling'
[  FAILED  ] SerialGridReductionTest.Scheduling (5669 ms)
[----------] 1 test from SerialGridReductionTest (5669 ms total)
```
This test runs with serial grid reduction, then with `gridReduce`. Each
time it runs two grid reductions. Both serial grid reductions succeed
because the semaphore buffer is properly zeroed. The `gridReduce`
succeeds the first time since the memory pool calls `at::zeros` again to
request a larger buffer size (`gridReduce` requires more semaphores
since there is one per thread segment vs one for each each block
segment). However, the second call to `gridReduce` fails because it has
not cleaned up its semaphores. Hacking that function to force
`PERSISTENT=1` would clean up the semaphores resulting in success in
this case. I'm leaving those kind of modifications for a follow-up.