fix: Cache id is not a valid dot node id

[JakubValtar]

Fixes cache to have a valid dot graph id.

• broken in refactor: Use UUID for UniqueID #23704

Before:

graph  polars_query {
  c7e2e5b86-a92c-4b63-8baf-b397a32ad8f2 -- p1
  p1[label="TABLE\nπ */1"]
  c7e2e5b86-a92c-4b63-8baf-b397a32ad8f2[label="CACHE"]
}

After:

graph  polars_query {
  "7e2e5b86-a92c-4b63-8baf-b397a32ad8f2" -- p1
  p1[label="TABLE\nπ */1"]
  "7e2e5b86-a92c-4b63-8baf-b397a32ad8f2"[label="CACHE"]
}

[ritchie46]

What was the problem?

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.59%. Comparing base (a67bf04) to head (dac5567).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/ir/dot.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24005      +/-   ##
==========================================
+ Coverage   81.57%   81.59%   +0.01%     
==========================================
  Files        1675     1675              
  Lines      225601   225708     +107     
  Branches     2897     2897              
==========================================
+ Hits       184040   184167     +127     
+ Misses      40834    40813      -21     
- Partials      727      728       +1     

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[JakubValtar]

In the UUID PR, the cache ID changed from a number (hex string) to UUID with dashes in it, and dashes are not allowed in dot node IDs without the ID being surrounded by quotes.