feat(py): Add more method to tuple object

[aisk]

Works as expected:

package main

import (
	"github.com/goplus/llgo/py"
	"github.com/goplus/llgo/py/std"
)

func main() {
	t := py.NewTuple(3)
	t.TupleSetItem(0, py.Str("111"))
	t.TupleSetItem(1, py.Str("222"))
	t.TupleSetItem(2, py.Str("333"))
	std.Print(t)
	s := t.TupleSlice(1, 3)
	std.Print(s)
}

$ ./llgo build -o a a.go
# command-line-arguments

$ ./a 
('111', '222', '333')
('222', '333')

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.58%. Comparing base (dfd85a7) to head (4b26dac).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #699   +/-   ##
=======================================
  Coverage   97.58%   97.58%           
=======================================
  Files          19       19           
  Lines        4600     4600           
=======================================
  Hits         4489     4489           
  Misses         94       94           
  Partials       17       17           

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