ci: increase Travis build resources to prevent timeouts

- Configure VM size to large for more computing resources

This change aims to resolve build timeouts during CI pipeline execution.

trie/trienode: store node blob to pebble db

- Introduced Pebble DB to store trie node blobs
- Modified `Node` structure to store only metadata (`Len`, `idx`)
- Replaced direct blob storage with `Blob()` method for retrieval
- Replaced `len(n.Blob)` with `n.Len`
- Used atomic counter for `idx` to ensure unique blob indexing
- Added `key()` method to generate unique keys for node storage
- Ensured memory cleanup with finalizers for deleted nodes
- Implemented `InitDB` function for database initialization
- Updated various database and trie operations to use new storage
- Adjusted tests and logging for compatibility with new approach
- Added `OpenTrieNodeBlobDB()` method to initialize `nodeblob` database
- Integrated `nodeblob` storage into `Node.OpenAndMergeDatabase()`

bump version to v1.5.606

bump version to v1.5.605

bump version to v1.5.604

bump version to v1.5.603

bump version to v1.5.602

bump verion to v1.5.601

triedb/pathdb: enlarge maxDiffLayers to 28800

* triedb/pathdb/database.go
  * Export maxDiffLayersto make this setting available for use in other packages
* triedb/pathdb/database_test.go
  * Adjust test cases to reflect the increased `maxDiffLayers` value
  * Update test logic to simulate and verify behavior with the increased `MaxDiffLayers` value.
* core/blockchain_test.go
  * Introduce `TestMaxDiffLayers` and `TestAdditionalLayers` constants to align with the updated `MaxDiffLayers`.
  * Adjust chain generation and pruning logic to reflect the enlarged `MaxDiffLayers`.

bump version to v1.5.500