feat(anthropic): support extended thinking round trips

[dailingtao]

Summary

Fixes #2219.

• map GenerateOptions.thinkingBudget to Anthropic budget_tokens
• preserve Anthropic thinking signatures and redacted thinking blocks in ThinkingBlock metadata
• restore those native blocks, in their original order, when conversation history is sent back to Anthropic
• preserve provider metadata while streaming thinking chunks are accumulated by ReasoningContext
• keep the existing text fallback for unsigned ThinkingBlocks from other providers
• document Anthropic extended-thinking configuration in English and Chinese

Validation

• mvn -pl agentscope-extensions/agentscope-extensions-model/agentscope-extensions-model-anthropic -am clean verify
• AgentScope Core: 2214 tests, 0 failures, 0 errors, 9 skipped
• Anthropic model extension: 150 tests, 0 failures, 0 errors, 1 skipped
• local JaCoCo estimate for added executable lines: 129/134 (96.3%)

[codecov]

Codecov Report

❌ Patch coverage is 86.56716% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...anthropic/formatter/AnthropicThinkingMetadata.java	75.60%	3 Missing and 7 partials ⚠️
...pe/core/agent/accumulator/ThinkingAccumulator.java	58.33%	2 Missing and 3 partials ⚠️
...l/anthropic/formatter/AnthropicResponseParser.java	95.58%	0 Missing and 3 partials ⚠️

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