Write integration tests and resolve issues found

[imlk0]

This PR aims to introduce an integration test module for proot-rs. #33

We use bats-core to run the integration tests. All the files are placed in the tests/ directory and README.md is included.

The current integration test includes these sections:

• cli: Test the command-line interface of proot-rs
• bind: Check if path bind is working correctly
• cwd: Testing the emulation of cwd
• multi-tracee: Testing for the multi-tracee case
• applets: Test some common applets (basically those listed here) to see if they work properly
  It should be noted that there are still 14 applets that have not been tested for some reason. They are chroot,df,dmesg,hostname,login,mount,passwd,reboot,su,top,umount,vi,watch,who. The reasons can be found in this table
• execve: Test the ability to run executable files
• event: Tests related to proot event loops

In the process of writing tests we found several bugs:

• Failed to execute statically linked binaries #37
• Binding a file to dir/file will result in a ENOTDIR: Not a directory #40
• Trailing slash is removed by proot-rs #41
• A call to unshare(CLONE_FS) from tracee may break the emulation of cwd. #42
• Processing the result of getdents64() #43
• thread 'main' panicked at 'get stopped tracee' #44

Four of the more serious ones have been fixed, the remaining two are less affected and have not been fixed yet

[oxr463]

@KB5201314 should we wait to merge until #42 and #43 are fixed?

[imlk0]

@KB5201314 should we wait to merge until #42 and #43 are fixed?

No, they're not that important, I think we can put them aside for now.