This reverts commit 04332b7.

Revert
#480
#481

### PR Description

This PR addresses the issue outlined in [Issue
#227](https://github.com/CentML/hidet/issues/227).

#### Problem:
After investigation, the problem arises because multiple threads were
writing to the same `fused_ir` directory. This led to race conditions
where one thread might attempt to delete a file that another thread had
already removed. Moreover, all candidates were being saved into a single
directory, resulting in overwriting of files across different threads.

#### Solution:
This commit introduces the following changes to resolve the issue:

1. **Separate Directories for Each Candidate**: 
- Each candidate now gets its own directory under `fuse_ir`, preventing
conflicts and file overwriting.
   
2. **Subdirectories for IRs by Candidate**:
- The `ir` files are now stored in separate subdirectories under
`candidate/ir`, ensuring that files from different candidates are
isolated.

3. **Test Case Added**:
- A new test case was introduced to verify that the number of folders in
`fuse_ir` matches the total number of candidates listed in
`candidate.txt`.

…rg#480)

### PR Description

This PR addresses the issue outlined in [Issue
hidet-org#227](CentML/hidet#227).

#### Problem:
After investigation, the problem arises because multiple threads were
writing to the same `fused_ir` directory. This led to race conditions
where one thread might attempt to delete a file that another thread had
already removed. Moreover, all candidates were being saved into a single
directory, resulting in overwriting of files across different threads.

#### Solution:
This commit introduces the following changes to resolve the issue:

1. **Separate Directories for Each Candidate**: 
- Each candidate now gets its own directory under `fuse_ir`, preventing
conflicts and file overwriting.
   
2. **Subdirectories for IRs by Candidate**:
- The `ir` files are now stored in separate subdirectories under
`candidate/ir`, ensuring that files from different candidates are
isolated.

3. **Test Case Added**:
- A new test case was introduced to verify that the number of folders in
`fuse_ir` matches the total number of candidates listed in
`candidate.txt`.