feat: Datastores and MessageTransforms in agent-spec

[youssef62]

Context
We want to have summarization transforms (ConversationSummarizationTransform and MessageSummarizationTransform) as native agent-spec components. For that we need to bring datastores to agent-spec OracleDatabaseDatastore, PostgresDatastore and InMemoryDatastore).

Changes

• Added components: OracleDatabaseDatastore, TlsOracleDatabaseConnectionConfig, MTlsOracleDatabaseConnectionConfig, PostgresDatabaseDatastore, TlsPostgresDatabaseConnectionConfig, InMemoryCollectionDatastore, MessageSummarizationTransform, and ConversationSummarizationTransform.
• Added tests in relevant files under tests/serialization/datastores/ and tests/serialization/transforms/.
• Fixed a deserialization issue that prevented use of Optional fields.

⚠️Note In changelog.rst the changes are described under the new features of 25.4.2 not in 26.1.1. Once 25.4.2 and 26.1.0 are released. I will rebase and update the changelog accordingly.

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[lfaucon]

Nice work 💯 Thanks

[lfaucon]

We will have to move the changelog entries to be within the correct release

[nasseur]

Internal regression succeeded 🍏: Build ID #87