feat: native bigint using math/big.Int #2678

Job	Run time
build (1.20.x, GOARCH=amd64 GOOS=linux, gno)	27s
build (1.20.x, GOARCH=wasm GOOS=js, gno)	25s
test (1.20.x, _test.cmd)	1m 7s
build (1.21.x, GOARCH=amd64 GOOS=linux, gno)	19s
test (1.20.x, _test.pkg)	49s
build (1.21.x, GOARCH=wasm GOOS=js, gno)	23s
test (1.20.x, _test.gnolang.native)	29s
test (1.20.x, _test.gnolang.stdlibs)	34s
test (1.20.x, _test.gnolang.realm)	36s
test (1.20.x, _test.gnolang.pkg0)	1m 42s
test (1.20.x, _test.gnolang.pkg1)	6m 20s
test (1.20.x, _test.gnolang.pkg2)	4m 10s
test (1.20.x, _test.gnolang.other)	29s
test (1.21.x, _test.cmd)	1m 4s
test (1.21.x, _test.pkg)	48s
test (1.21.x, _test.gnolang.native)	31s
test (1.21.x, _test.gnolang.stdlibs)	41s
test (1.21.x, _test.gnolang.realm)	37s
test (1.21.x, _test.gnolang.pkg0)	1m 34s
test (1.21.x, _test.gnolang.pkg1)	5m 55s
test (1.21.x, _test.gnolang.pkg2)	3m 56s
test (1.21.x, _test.gnolang.other)	31s
upload-coverage	0s
	33m 27s

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