Added default path flow

[0xKrishna]

Major changes:

1. Storage abstraction layer (storage.go)

Introduces Storage[AppTx, R] struct that consolidates all databases (appchain, txpool, txbatch) and components (multichain, subscriber) with unified lifecycle management and accessor methods.

2. Standardized path hierarchy (paths.go)

Defines three-layer data directory structure (multichain/{chainID}/, consensus/txbatch/{chainID}/, appchain/db/) with helper functions for consistent path resolution across SDK and pelacli.

3. One-call initialization (init.go)

InitApp() orchestrates full appchain bootstrap—waits for required chains, opens all databases, creates multichain accessor and subscriber—reducing ~60 lines of boilerplate to one function call.

[0xKrishna]

Related example PR : 0xAtelerix/example#14

There are also changed in pelacli regarding default multichain and ext-network config for which I will raise PR once the SDK PR is finalized and merged.

[github-actions]

Code Metrics Report

	#32 (bfb63d8)	#32 (12600cf)	+/-
Coverage	58.7%	58.7%	0.0%
Code to Test Ratio	1:0.4	1:0.4	-0.1
Test Execution Time	1m6s	1m6s	0s

Details

  |                     | #32 (bfb63d8) | #32 (12600cf) | +/-  |
  |---------------------|---------------|---------------|------|
  | Coverage            |         58.7% |         58.7% | 0.0% |
  |   Files             |            56 |            56 |    0 |
  |   Lines             |          2902 |          2902 |    0 |
  |   Covered           |          1706 |          1706 |    0 |
- | Code to Test Ratio  |         1:0.4 |         1:0.4 | -0.1 |
  |   Code              |         13642 |         13651 |   +9 |
  |   Test              |          6359 |          6359 |    0 |
  | Test Execution Time |          1m6s |          1m6s |   0s |

Code coverage of files in pull request scope (40.7% → 40.7%)

Files	Coverage	+/-	Status
gosdk/appchain.go	30.0%	0.0%	modified
gosdk/init.go	59.5%	0.0%	added
gosdk/mdbx_event_wrapper.go	6.3%	0.0%	modified
gosdk/multichain.go	76.6%	0.0%	modified
gosdk/multichain_sql.go	61.4%	0.0%	modified
gosdk/paths.go	88.8%	0.0%	added
gosdk/receipt/receipt.go	76.9%	0.0%	modified
gosdk/state_transition.go	1.7%	0.0%	modified
gosdk/storage.go	52.4%	0.0%	added

---

Reported by octocov