fix: retrieve multiple text contentBlock in messageConent

[poshinchen]

Description

Our sessionMapper only reads and parse the first text contentBlock, but there are cases where multiple multiple text contentBlocks exists. Therefore adjust the parsing logic to detect multiple text contentBlocks.

Note:
multi-modal contentBlcoks parsing is out of scope as multi-modal support will be visited in the future.

Related Issues

#130

Documentation PR

N/A

Type of Change

Bug fix

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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