[PyTorch] Avoid using std::regex for device string parsing in Device.cpp (#63204)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63204
Currently, `std::regex` is used for parsing device strings. This is undesirable for a few reasons.
1. Increases binary size
2. Slows down model loading
3. Potentially uses more memory at runtime
4. Takes marginally longer time to build code that uses std::regex v/s not using std::regex
This change avoids the use of `std::regex` for parsing the device string since we don't need to.
ghstack-source-id: 136006963
Test Plan:
### AI Bench Runs
**Before this change:**
1. Model Load time: [252ms](https://www.internalfb.com/intern/aibench/details/332471502816548)
2. Model unload time: 3.5ms
**After this change:**
1. Model Load time: [240ms](https://www.internalfb.com/intern/aibench/details/652195589031318), which is an approx 5% reduction for the current model. I suspect percentage wise, it will be larger for smaller models since this is a fixed cost reduction.
2. Model unload time: 3.3ms (probably too small to be meaningfully impactful to an end user).
### BSB Results
```
D30281388-V1 (https://www.internalfb.com/intern/diff/D30281388/?dest_number=135713848)
messenger-pika-optimized-device: Succeeded
Change in Download Size for arm64 + 3x assets variation: -7.1 KiB
Change in Uncompressed Size for arm64 + 3x assets variation: -17.6 KiB
Mbex Comparison: https://our.intern.facebook.com/intern/mbex/bsb:551399955987465@base/bsb:551399955987465@diff/
```
Reviewed By: raziel
Differential Revision: D30281388
fbshipit-source-id: 4d998e9f313e6366d9d89a6a73cd090ddfb059fc
