Add per-source telemetry for package IDs containing non-alphanumeric, dash, dot, or underscore characters

[Copilot]

Bug

Fixes: NuGet/Home#14212

Description

Adds telemetry to track whether any package ID contains characters outside [A-Za-z0-9.\-_] (i.e., anything other than ASCII letters, digits, ., or -, _). This is emitted in two places:

1. Per-source (PackageSourceDiagnostics event) — correlates non-standard ID usage to specific feed providers
2. Per-restore (ProjectRestoreInformation event) — indicates whether any resolved package in the restore graph has a non-standard ID

Protocol layer

• Added PackageId property to ProtocolDiagnosticNupkgCopiedEvent (nullable; new 3-param constructor, old 2-param delegates to it)
• Updated all four raise-sites to pass the package ID:
  • FindPackagesByIdNupkgDownloader → identity.Id
  • LocalPackageArchiveDownloader → _packageIdentity.Id
  • LocalV3FindPackageByIdResource / LocalV2FindPackageByIdResource → id parameter
• New public API declared in both PublicAPI.Unshipped.txt files

Per-source telemetry (PackageSourceTelemetry)

• Data class: new IdContainsNonAsciiCharacter bool, sticky-true once any non-standard ID is seen for that source
• Detection uses a zero-allocation ReadOnlySpan<char> character loop (local function HasNonASCIICharacters)
• AddNupkgCopiedData: skips check when PackageId is null (events raised by old constructor)
• ToTelemetryAsync: emits nupkgs.idcontainsnonasciicharacter alongside the existing nupkgs.copied / nupkgs.bytes

Per-restore telemetry (RestoreCommand)

• New AnyPackageIdContainsNonASCIICharacters property on the ProjectRestoreInformation telemetry event
• Scans all resolved packages across non-conflicting restore graphs using the same character-check logic (local function)
• Only emitted for non-NoOp restores (NoOp returns before this code runs)

Tests

PackageSourceTelemetryTests — Existing tests covering AddNupkgCopiedData for: all-standard IDs → false; non-standard IDs (underscore, Unicode, space, @, +) → true; mixed batch with one non-standard → sticky true; null PackageId → false. ToTelemetry_WithData_CreatesTelemetryProperties asserts the new property is emitted.

RestoreCommandTests — New tests:

• ExecuteAsync_WithASCIIPackageId_AnyPackageIdContainsNonASCIICharactersIsFalse — standard [A-Za-z0-9.-] package → false
• ExecuteAsync_WithNonASCIIPackageId_AnyPackageIdContainsNonASCIICharactersIsTrue — [Theory] with underscore, Kelvin sign (U+212A), Greek alpha (U+03B1), accented Latin (U+00E9), Cyrillic (U+0410) → true
• ExecuteAsync_WithMixedPackageIds_AnyPackageIdContainsNonASCIICharactersIsTrue — [Theory] where direct dep is standard but transitive dep has non-standard chars → true
• Updated existing exhaustive telemetry tests to include the new property

PR Checklist

• Meaningful title, helpful description and a linked NuGet/Home issue
• Added tests
• Link to an issue or pull request to update docs if this PR changes settings, environment variables, new feature, etc.

[nkolev92]

@copilot
This needs rebased to fix the nullability warnings.

[Copilot]

@copilot
This needs rebased to fix the nullability warnings.

Fixed in 5a894ff. The changes incorporate dev's nullability Phase 1 work for ProtocolDiagnosticNupkgCopiedEvent:

• Removed #nullable disable from ProtocolDiagnosticNupkgCopiedEvent.cs
• PackageId property and packageId constructor parameter are now string?
• PublicAPI.Shipped.txt (both TFMs): replaced the old ~ entries for Source and the 2-param constructor with properly-annotated string! entries (matching what dev's nullability PR added)
• PublicAPI.Unshipped.txt (both TFMs): replaced ~ entries with fully-annotated forms (string? for PackageId, string!/string? for the 3-param constructor)

Build: 0 warnings, 0 errors.