Fix GetConfigParams query

[mnogoborec]

Fix liteserver GetConfigParams query with CFG_FROM_PREV_KEY_BLOCK mode

[Copilot]

Pull request overview

This PR fixes the GetConfigParams liteserver query to properly handle the CFG_FROM_PREV_KEY_BLOCK mode, which retrieves configuration from a previous key block instead of the current block state.

Changes:

• Consolidates the get_all_config_params function into a more flexible get_config_params function that handles both regular config retrieval and retrieval from previous key blocks
• Implements a new get_prev_key_block function that locates the previous key block for a given block ID using the masterchain state's prev_blocks information
• Adds support for the CFG_NEED_PREV_BLOCKS flag to conditionally include prev_blocks validation in config retrieval
• Updates the GetConfigAll query handler to use the new unified function
• Extends test utilities to support prev_blocks configuration in master state generation
• Adds comprehensive test coverage for key block resolution with proper edge case handling (blocks before key blocks should fail)

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/node/src/network/liteserver.rs	Consolidates config retrieval logic, implements key block resolution with proper error handling, and updates query handlers
src/node/src/tests/test_helper.rs	Adds prev_blocks field to GenMasterStateParams and implements support for populating prev_blocks in generated master states
src/node/src/tests/test_liteserver.rs	Adds comprehensive test with helper function to verify CFG_FROM_PREV_KEY_BLOCK mode works correctly with proper key block lookup and error cases

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