feat: update plugin-code-execution to version 0.0.4 and change mode t…

[yaonyan]

This pull request updates the code execution plugin and its dependencies to use a standardized execution mode identifier. The main change is the replacement of the previously used custom string "custom" with the new explicit mode "code_execution" throughout the plugin, examples, documentation, and tests. Additionally, the plugin and core package versions are bumped to reflect these changes.

Standardization of execution mode:

• Replaced all instances of mode: "custom" with mode: "code_execution" in the plugin application logic (plugin.ts), examples (examples/basic-usage.ts), documentation (README.md), and tests (code_execution.test.ts). This ensures consistent identification and usage of the code execution mode across the codebase. [1] [2] [3] [4] [5] [6]

• Updated the ExecutionMode type definition in types.ts to allow any string value, removing the special "custom" literal and supporting future extensibility.

Version updates:

• Bumped the version of the @mcpc/core package from 0.3.4 to 0.3.5 in both its own manifest and as a dependency in the plugin. [1] [2]
• Bumped the version of the @mcpc/plugin-code-execution package from 0.0.3 to 0.0.4.