chore: explicitly cast LONG_MAX to double

[codebytere]

Fixes a compilation error encountered in Electron as a result of Chromium enabling the -Wimplicit-const-int-float-conversion compilation flag in this CL.

Compilation Failure

../../third_party/squirrel.mac/vendor/ReactiveObjC/ReactiveObjC/RACQueueScheduler.m:52:62: error: implicit conversion from 'long' to 'double' changes value from 9223372036854775807 to 9223372036854775808 [-Werror,-Wimplicit-const-int-float-conversion]
                .tv_nsec = (long)fmin(fmax(frac * NSEC_PER_SEC, LONG_MIN), LONG_MAX)
                                 ~~~~                                      ^~~~~~~~
../../third_party/llvm-build/Release+Asserts/lib/clang/13.0.0/include/limits.h:47:19: note: expanded from macro 'LONG_MAX'
#define LONG_MAX  __LONG_MAX__
                  ^~~~~~~~~~~~
<built-in>:53:22: note: expanded from here
#define __LONG_MAX__ 9223372036854775807L
                     ^~~~~~~~~~~~~~~~~~~~
../../third_party/squirrel.mac/vendor/ReactiveObjC/ReactiveObjC/RACQueueScheduler.m:51:51: error: implicit conversion from 'long' to 'double' changes value from 9223372036854775807 to 9223372036854775808 [-Werror,-Wimplicit-const-int-float-conversion]
                .tv_sec = (time_t)fmin(fmax(seconds, LONG_MIN), LONG_MAX),
                                  ~~~~                          ^~~~~~~~
../../third_party/llvm-build/Release+Asserts/lib/clang/13.0.0/include/limits.h:47:19: note: expanded from macro 'LONG_MAX'
#define LONG_MAX  __LONG_MAX__
                  ^~~~~~~~~~~~
<built-in>:53:22: note: expanded from here
#define __LONG_MAX__ 9223372036854775807L
                     ^~~~~~~~~~~~~~~~~~~~
2 errors generated.

Please let me know if I need to make other associated changes or you all would prefer another approach to fixing this issue!