[HUDI-7341] Support unmerged record read

[linliu-code]

Change Logs

Created a new record buffer to store unmerged records.

Impact

Some workload can be supported.

Risk level (write none, low medium or high below)

Low.

Documentation Update

Describe any necessary documentation update if there is any new feature, config, or user-facing change

• The config description must be updated if new configs are added or the default value of the configs are changed
• Any new feature or user-facing change requires updating the Hudi website. Please create a Jira ticket, attach the ticket number here and follow the instruction to make changes to the website.

Contributor's checklist

• [ ] Read through contributor's guide
• [ ] Change Logs and Impact were stated clearly
• [ ] Adequate tests were added if applicable
• [ ] CI passed

[hudi-bot]

CI report:

• 8a0aba2e0e7dcea9c3d7c3c9d81d92d5585cd768 Azure: SUCCESS

Bot commands

@hudi-bot supports the following commands:

• @hudi-bot run azure re-run the last Azure build