test: add regression tests for issues #287 and #341

[robert-j-y]

Description

Adds e2e regression tests for two fixed issues:

Issue #287 - Tool calls with missing arguments field

• Tests that tool calls work correctly when upstream providers omit the arguments field for tools with no parameters
• Previously caused AI_TypeValidationError because the schema required arguments to be a string
• Uses anthropic/claude-3.5-haiku (mentioned in original issue context as potentially omitting the arguments field)

Issue #341 - Cache control only applies to last text part

• Tests that message-level cache_control works correctly with multi-part messages on Anthropic models
• Previously applied cache_control to ALL parts, which could exceed provider cache segment limits
• Uses anthropic/claude-3.5-haiku which supports cache control

Updates since last revision

• Changed issue Tool calls missing arguments field causing AI_TypeValidationError (anthropic haiku-4.5) #287 test to use anthropic/claude-3.5-haiku instead of openai/gpt-4o-mini to match the original issue context (Anthropic Haiku was noted as potentially omitting the arguments field)

Human Review Checklist

• Verify test scenarios match the original issue reports ( Tool calls missing arguments field causing AI_TypeValidationError (anthropic haiku-4.5) #287, Bug: Message-level cache_control applied to all content parts, exceeding Anthropic's 4-segment limit #341)
• Confirm model choice for Tool calls missing arguments field causing AI_TypeValidationError (anthropic haiku-4.5) #287 (anthropic/claude-3.5-haiku) is appropriate based on original issue context
• Tests couldn't be verified locally due to missing env vars - confirm CI passes

Checklist

• I have run pnpm stylecheck and pnpm typecheck
• I have run pnpm test and all tests pass
• I have added tests for my changes (if applicable)
• I have updated documentation (if applicable) - N/A

Changeset

• I have run pnpm changeset to create a changeset file

Note: Used pnpm changeset --empty since this is a test-only change that doesn't need a release.

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Link to Devin run: https://app.devin.ai/sessions/ad14476ac9334b8a962f771f56e48975
Requested by: Robert Yeakel (@robert-j-y)