fix: fix same file copy

[fatelei]

if restart the dify sandbox, python env is keeped, you will meet the panic error

cp: '/usr/lib/python3/dist-packages/linkify_it/__pycache__/ucre.cpytho
n-313.pyc' and '/var/sandbox/sandbox-python//usr/lib/python3/dist-pack
ages/linkify_it/__pycache__/ucre.cpython-313.pyc' are the same file
cp: '/usr/lib/python3/dist-packages/linkify_it/tlds.py' and '/var/sand
box/sandbox-python//usr/lib/python3/dist-packages/linkify_it/tlds.py' 
are the same file
cp: '/usr/lib/python3/dist-packages/linkify_it/main.py' and '/var/sand
box/sandbox-python//usr/lib/python3/dist-packages/linkify_it/main.py' 
are the same file
2025/12/29 16:46:54 server.go:58: [PANIC]failed to initialize python 
dependencies sandbox: exit status 1
panic: 

goroutine 18 [running]:
github.com/langgenius/dify-sandbox/internal/utils/log.(*Log).Panic(...
)
    /home/fatelei/go/src/github.com/fatelei/dify-sandbox/internal/util
s/log/core.go:55
github.com/langgenius/dify-sandbox/internal/utils/log.Panic({0x500aeb?
, 0x0?}, {0x400005cfb0?, 0x0?, 0x0?})
    /home/fatelei/go/src/github.com/fatelei/dify-sandbox/internal/util
s/log/core.go:209 +0x74
github.com/langgenius/dify-sandbox/internal/server.initDependencies()
    /home/fatelei/go/src/github.com/fatelei/dify-sandbox/internal/serv
er/server.go:58 +0xe8
created by github.com/langgenius/dify-sandbox/internal/server.Run in 
goroutine 1
    /home/fatelei/go/src/github.com/fatelei/dify-sandbox/internal/serv
er/server.go:97 +0x28

here we should skip the same file to copy