```
`ArgsManager::m_cached_blocks_path` is protected by
`ArgsManager::cs_args` and returning a reference to it after releasing
the mutex is unsafe.
To resolve this, return a copy of the path. This has some performance
penalty which is presumably ok, given that paths are a few 100s bytes
at most and `GetBlocksDirPath()` is not called often.
This silences the following (clang 18):
common/args.cpp:288:31: error: returning variable 'm_cached_blocks_path' by reference requires holding mutex 'cs_args' [-Werror,-Wthread-safety-reference-return]
288 | if (!path.empty()) return path;
| ^
```
Do the same with
`ArgsManager::GetDataDir()`,
`ArgsManager::GetDataDirBase()` and
`ArgsManager::GetDataDirNet()`.
```
Partial backport of core#29040:
https://github.com/bitcoin/bitcoin/pull/29040/commits/856c88776f8486446602476a1c9e133ac0cff510