refactor(hook): change PreCallEvent related comments from read-only to modifiable, aligning with PreReasoningEvent

[jujn]

Description

This PR updates PreCallEvent to be modifiable (revising the previous read-only comments), and aligns its inputMessages handling with PreReasoningEvent.

Checklist

Please check the following items before code is ready to be reviewed.

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (e.g. links, examples, etc.)
• Code is ready for review

[Copilot]

Pull request overview

This PR updates hook documentation and behavior so PreCallEvent is treated as a modifiable hook event (similar to PreReasoningEvent), allowing hooks to alter the input message list before the agent processes it.

Changes:

• Mark PreCallEvent as modifiable and document getInputMessages/setInputMessages.
• Copy inputMessages on PreCallEvent construction and enforce non-null inputs.
• Update Hook Javadoc to list PreCallEvent among modifiable events (and remove it from notification-only events).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
agentscope-core/src/main/java/io/agentscope/core/hook/PreCallEvent.java	Makes PreCallEvent input messages modifiable and aligns list handling with other modifiable events.
agentscope-core/src/main/java/io/agentscope/core/hook/Hook.java	Updates hook documentation to categorize PreCallEvent as a modifiable event.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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