build(deps): update ic-agent, ic-utils, pocket-ic, and dfx (#59)

## Summary
- Update ic-agent from 0.44 to 0.45
- Update ic-utils from 0.44 to 0.45  
- Update pocket-ic from 6.0 to 12.0
- Update dfx from 0.20.0 to 0.30.2
- Update pocket-ic download script to 12.0.0

## Test plan
- [x] All Rust unit tests passing (8/8)
- [x] All Rust integration tests passing (19/19)
  - [x] Custom assets canister test
  - [x] Protocol error / rate limiting test
  - [x] Range request streaming tests
- [x] Total: 27/27 tests passing (100%)

Author: shilingwang

.github/workflows/build-and-test.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Install PocketIC server
         uses: dfinity/pocketic@main
         with:
-          pocket-ic-server-version: '7.0.0'
+          pocket-ic-server-version: '12.0.0'
 
       - name: Confirm successful installation
         run: ${POCKET_IC_BIN} --version