Performance freeze when opening parent namespace page due to automatic deep-expansion of child blocks

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### Search first

- [x] I searched and no similar issues were found

### What Happened?

Similar to #619 (However, #619 also specifies properties being expanded, whereas this focus is strictly on block depth expansion)

When opening a parent namespace page that contains a massive hierarchy of sub-pages and blocks, Logseq attempts to fully expand every single child block/page. For large graphs, this causes the application to freeze entirely.

For example: I have a namespace that goes like Pathology/Category 1/Category 2/Specific entity
If I try to open Pathology then the page essentially freezes because i have around 20k blocks in total when you combine all the subcategories and Logseq tries to open all the child blocks.

### Reproduce the Bug

1. Create a namespace with multiple children
2. You will see that in the most upper level namespace every single entity is displayed

### Expected Behavior

You can control to what depth the children nodes are shown

### Screenshots

### Files

_No response_

### Browser, Desktop or Mobile Platform Information

macOS, latest overnight build

### Additional Context

_No response_

### Are you willing to submit a PR? If you know how to fix the bug.

- [ ] I'm willing to submit a PR (Thank you!)

Start by reproducing the freeze with a namespace containing a large, deeply nested hierarchy, using the macOS overnight build described in the issue. Trace the code responsible for expanding child pages and blocks when opening the parent namespace; done means opening remains responsive and child visibility can be limited by depth.

Written by the indexing model from the issue text.