Improve exception logging and telemetry for hydration status

[tyrielv]

• Thread ITracer through EnlistmentHydrationSummary.CreateSummary()
• Add Stopwatch timing per phase with HydrationSummaryDuration telemetry
• Log RelatedWarning on early exit with specific invalid count values
• Log RelatedError in catch block with elapsed duration
• Add exception handling to LoadModifiedPaths file fallback with ITracer
• Add null check in ReadModifiedPathDatabaseLines to prevent NRE

[KeithIsSleeping]

see below

[KeithIsSleeping]

(Corrected re-post — the original review had rendering issues with backtick escaping)

Good changes overall — solid observability improvement. A few notes:

1. Breaking signature change on CreateSummary — ITracer tracer was added as a required (non-optional) parameter. If any callers exist outside this repo (e.g., in the hooks path or downstream consumers), they'll fail at compile time. Worth verifying there are no other callers. (PR Add CancellationToken and async hydration to GitStatusCache #1914 adds CancellationToken as optional with = default, but ITracer here is required.)

2. Broadened pipe exception catch — TryLoadModifiedPathsFromPipe changed from catch (BrokenPipeException) to catch (Exception). This now catches things like ArgumentException, InvalidOperationException, etc. that may indicate programming errors rather than pipe communication failures. Consider catch (IOException) or catch (BrokenPipeException) + catch (TimeoutException) for a tighter net, or at minimum log at Warning level (which you do — good) so these don't go unnoticed.

3. Nit — The GetHeadTreeCount error messages use \nOutput: (single newline) and \n\nError: (double newline) inconsistently.

The per-phase Stopwatch timing with EmitDurationTelemetry is particularly well done — will make diagnosing slow phases trivial. The early-exit validation before the expensive GetHeadTreeCount is a smart optimization. The null check in ReadModifiedPathDatabaseLines fixes a real latent NRE.

Looks good to merge.