Fix: Prevent cross-contamination of cache data across analysis modes

[wpfleger96]

Summary

This PR fixes a cache contamination bug where the analyze tool's (from Developer extension) LRU cache would incorrectly return cached results from one analysis mode (e.g., Structure) when a different mode (e.g., Semantic) was requested. The root cause was that the cache key only included the file path and modification time, but not the analysis mode, allowing different modes to overwrite each other's cached data.

The fix adds the AnalysisMode enum as a third component to the CacheKey struct, ensuring that each combination of (path, modified time, mode) creates a separate cache entry. This prevents Structure mode's lightweight directory data from contaminating Semantic mode's detailed AST analysis results, which was problematic when both modes were used sequentially in the same session and would cause the tool to return incomplete results.

Type of Change

• Feature
• Bug fix
• Refactor / Code quality
• Performance improvement
• Documentation
• Tests
• Security fix
• Build / Release
• Other (specify below)

Testing

I added a unit test for validating cache separation, and I also tested this manually on a local codebase

Related Issues

Fixes #5074

[wpfleger96]

Now when I run the same test that I did in #5074, we see the complete and accurate results:

Yes! This time the focused analysis found more complete results. The key improvements are:

**Better Coverage:**
- **11 incoming chains** (vs 10 previously) - now includes the cross-package reference
- **3 files analyzed** (F1, F2, F3) instead of just 2

**Cross-Package Reference Found:**
- `F1:23` - This is the reference in `/Users/wpfleger/Development/oncall-buddy/cmd/main.go` at line 23, which corresponds to the `Run *oncallbuddy.RunCmd` field we found with ripgrep

**Complete File Mapping:**
- F1: `/Users/wpfleger/Development/oncall-buddy/cmd/main.go` (the main command structure)
- F2: `/Users/wpfleger/Development/oncall-buddy/pkg/oncallbuddy/main.go` (where RunCmd is defined)
- F3: `/Users/wpfleger/Development/oncall-buddy/pkg/oncallbuddy/main_test.go` (the test file)

**Definition Location:**
- Shows `F2:87 - RunCmd` which correctly identifies the struct definition at line 87 in the main.go file

So this second run captured the complete picture of the `RunCmd` symbol, including:
1. The struct type definition (line 87)
2. All its methods and their call chains
3. The cross-package reference from cmd/main.go
4. All test references

[tlongwell-block]

Confirmed the bug and the fix locally