Add dylint lint library for Zed-specific patterns (#58496)

Adds a dylint library under tooling/lints that flags Zed-specific
anti-patterns:

* shared_string_from_str_literal, 
* async_block_without_await, 
* entity_update_in_render, 
* notify_in_render, 
* owned_string_into_shared, 
* len_in_loop_condition, and 
* blocking_io_on_foreground. 

Includes UI tests, a single-lint helper, and workspace.metadata.dylint
registration so cargo dylint --all discovers it. The library pins its
own nightly toolchain (kept out of the main workspace) and tracks dylint
6.

Release Notes:

- N/A

Self-Review Checklist:

- [ ] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A or Added/Fixed/Improved ...

.agents/skills/lint-creator/SKILL.md

@@ -0,0 +1,17 @@
+---
+name: lint-creator
+description: An auxiliary skill to add more dylints to `tooling/lints`
+disable-model-invocation: false
+---
+
+# Lint RULES
+
+1. Every lint MUST have accompanying `ui` tests
+2. `ui` tests MUST be in the `ui` folder
+3. Every lint MUST be in a separate module
+4. Every lint MUST have negative `ui` tests
+5. Lints should be as simple as possible.
+6. Reporting is fine if it's simple, it does not need to be elaborate or lengthy code.
+7. Do NOT suggest how to fix the lint, only flag it.
+8. Do NOT make lints machine applicable.
+9. Detect if lints are redundant vs clippy's capabilities.