purego: add benchmarks for calling methods

[tmc]

Add benchmarks comparing SyscallN, RegisterFunc, and callback performance across different argument counts.
This helps measure and compare the overhead of different calling approaches in purego's function invocation system.

Closes #362

Current output:

goos: linux
goarch: arm64
pkg: github.com/ebitengine/purego
BenchmarkCallingMethods/RegisterFunc/Callback/1args-4            3150840               345.5 ns/op            96 B/op          6 allocs/op
BenchmarkCallingMethods/RegisterFunc/Callback/2args-4            3140649               415.8 ns/op           152 B/op          7 allocs/op
BenchmarkCallingMethods/RegisterFunc/Callback/3args-4            1962769               622.9 ns/op           224 B/op          8 allocs/op
BenchmarkCallingMethods/RegisterFunc/Callback/5args-4            2104015               549.3 ns/op           336 B/op         10 allocs/op
BenchmarkCallingMethods/RegisterFunc/Callback/10args-4           1280574              1162 ns/op             600 B/op         15 allocs/op
BenchmarkCallingMethods/RegisterFunc/Callback/14args-4            787353              1330 ns/op             888 B/op         19 allocs/op
BenchmarkCallingMethods/RegisterFunc/Callback/15args-4           1000000              1087 ns/op             928 B/op         20 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/1args-4               7312062               179.1 ns/op            40 B/op          3 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/2args-4               4575436               259.8 ns/op            72 B/op          4 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/3args-4               5702834               203.9 ns/op           112 B/op          5 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/5args-4               4748464               357.9 ns/op           176 B/op          7 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/10args-4              2852462               384.0 ns/op           328 B/op         12 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/14args-4              2587800               679.0 ns/op           472 B/op         16 allocs/op
BenchmarkCallingMethods/RegisterFunc/CFunc/15args-4              2343153               482.9 ns/op           512 B/op         17 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/1args-4                5052274               268.1 ns/op            56 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/2args-4                3734990               331.6 ns/op            80 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/3args-4                3882723               302.8 ns/op           112 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/5args-4                3444187               405.1 ns/op           160 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/10args-4               1766395               624.9 ns/op           272 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/14args-4               2003835               598.1 ns/op           416 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/Callback/15args-4               1750140               848.6 ns/op           416 B/op          3 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/1args-4                  23856542                49.10 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/2args-4                  25922942                46.47 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/3args-4                  25489951                49.48 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/5args-4                  24297174                51.78 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/10args-4                 23921144                48.11 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/14args-4                 24247138                52.55 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/SyscallN/CFunc/15args-4                 22587331                58.45 ns/op            0 B/op          0 allocs/op
BenchmarkCallingMethods/RoundTrip/1args-4                        4651420               222.7 ns/op            56 B/op          3 allocs/op
BenchmarkCallingMethods/RoundTrip/2args-4                        4831054               257.3 ns/op            80 B/op          3 allocs/op
BenchmarkCallingMethods/RoundTrip/3args-4                        3868870               380.7 ns/op           112 B/op          3 allocs/op
BenchmarkCallingMethods/RoundTrip/5args-4                        3571844               327.6 ns/op           160 B/op          3 allocs/op
BenchmarkCallingMethods/RoundTrip/10args-4                       2216022               608.3 ns/op           272 B/op          3 allocs/op
PASS
ok      github.com/ebitengine/purego    57.446s

[hajimehoshi]

The benchmark doesn't use C functions. Using C functions in a dynamic library would be more meaningful to test actual cases in the real world.

[tmc]

The benchmark doesn't use C functions. Using C functions in a dynamic library would be more meaningful to test actual cases in the real world.

will extend the callbacks to not be the go no-ops but c calls

[tmc]

done.

note: this uses long+uintptr because of the bug addressed in #360