feat: non-deterministic function detection and temporal improvements

[AviAvni]

Summary

Split from #359.

• Add non_deterministic field to GraphFn struct for tracking functions with non-deterministic output
• Extend cypher_fn! macro with variants for non-deterministic functions
• Implement plan_is_non_deterministic() — walks execution plan tree to detect non-deterministic function calls (needed by effects replication to decide whether to use effects or full re-execution)
• Add zero-arg temporal overloads: date(), localtime(), localdatetime() returning current time
• Add .transaction() temporal variants using Runtime::transaction_timestamp for consistent values within a transaction
• Mark rand(), randomUUID(), timestamp() and temporal functions as non-deterministic

Test plan

• cargo check passes
• Temporal zero-arg functions return current date/time
• plan_is_non_deterministic() correctly identifies plans with rand/timestamp calls

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 5e00d1b3-964c-4022-b169-0577f49ec740

📥 Commits

Reviewing files that changed from the base of the PR and between d51f96e and 7b5d756.

📒 Files selected for processing (7)

• graph/src/planner/mod.rs
• graph/src/runtime/functions/aggregation.rs
• graph/src/runtime/functions/conversion.rs
• graph/src/runtime/functions/math.rs
• graph/src/runtime/functions/mod.rs
• graph/src/runtime/functions/temporal.rs
• graph/src/runtime/runtime.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch non-deterministic-functions

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[codecov]

Codecov Report

❌ Patch coverage is 13.67521% with 101 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.90%. Comparing base (d51f96e) to head (7b5d756).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
graph/src/planner/mod.rs	0.00%	75 Missing ⚠️
graph/src/runtime/functions/temporal.rs	26.47%	25 Missing ⚠️
graph/src/runtime/functions/mod.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #376      +/-   ##
==========================================
- Coverage   84.15%   83.90%   -0.26%     
==========================================
  Files         110      110              
  Lines       28963    29077     +114     
==========================================
+ Hits        24375    24397      +22     
- Misses       4588     4680      +92     

Flag	Coverage Δ
fuzz	41.96% <13.67%> (+0.08%)	⬆️

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