…be path matching

Probe source paths are sometimes delivered by IDE tooling that does not
match the on-disk casing (DEBUG-5107) or uses Windows-style backslash
separators (DEBUG-5111). The line probe path matcher previously rejected
both, so probes never moved past RECEIVED to INSTALLED in those cases.

In `Utils.path_matches_suffix?`, downcase both the actual file path and
the user-supplied suffix, and translate backslashes in the suffix to
forward slashes before comparing. In `Utils.path_can_match_spec?`,
normalize backslashes in the spec up-front so the "/+" regex used to
peel off leading directory components keeps working when the user
supplies a Windows-style path.

The unconditional bug markers for
`Test_Debugger_Line_Probe_Statuses::test_probe_status_log_line_with_different_casing`
and `::test_probe_status_log_line_with_windows_path` in
DataDog/system-tests `manifests/ruby.yml` can be removed once this lands.

Address review comment on PR #5754: the previous unconditional downcase
in path_matches_suffix? made matching always case-insensitive, which
contradicted the design comment in the same file (steps 5-6 case-sensitive,
steps 7-8 case-insensitive fallback). On case-sensitive deployments with
two files differing only by case (e.g. /app/foo.rb and /app/FOO.rb), a
correctly-cased probe path like foo.rb would match both, surfacing as
MultiplePathsMatch — a regression vs the pre-PR behavior.

Restore the documented ordering:
- Utils.path_matches_suffix? gains case_insensitive: keyword (defaults to
  case-sensitive); backslash normalization remains unconditional.
- Utils.path_can_match_spec? runs the suffix-shortening loop twice,
  case-sensitive first.
- CodeTracker#iseqs_for_path_suffix and #resolve_path_suffix run two passes,
  case-sensitive first, case-insensitive fallback.
- Instrumenter#raise_if_probe_in_loaded_features tries $LOADED_FEATURES.find
  case-sensitive first, case-insensitive fallback.

Specs:
- spec/datadog/di/utils_spec.rb covers case-sensitive default behavior and
  the case_insensitive: true parameter explicitly.
- spec/datadog/di/code_tracker_spec.rb covers the case-different-paths
  scenario directly: unique match on correctly-cased lookup, fallback when
  no case-sensitive match exists, MultiplePathsMatch when the fallback is
  ambiguous.

Verified: standardrb clean, steep clean, full spec/datadog/di/utils_spec.rb,
spec/datadog/di/code_tracker_spec.rb, spec/datadog/di/instrumenter_spec.rb,
spec/datadog/di/probe_spec.rb pass (200 examples).

Co-Authored-By: Claude <[email protected]>

The DEBUG-5111 Windows path fix was incomplete: Utils.path_matches_suffix?
normalizes backslashes internally, but CodeTracker#iseqs_for_path_suffix
and #resolve_path_suffix have their own suffix-shortening loops that check
working_suffix.include?('/') and strip via %r{.*/+}. When the probe path
contains only backslashes (e.g. shared\rails\app\foo.rb sent by IDE tooling
on Windows), the loop's '/' check is false, so the stripping never fires.
With no stripping, only the full suffix is tested against registry paths;
the typical Linux deployment doesn't have the source-repo prefix
(shared/rails/) in its filesystem paths, so the match fails and the probe
stays at RECEIVED instead of progressing to INSTALLED.

Surfaced via the system test test_probe_status_log_line_with_windows_path
in DataDog/system-tests, which sends sourceFile with backslashes against a
Rails weblog whose runtime paths lack the shared/rails/ prefix.

Fix: normalize backslashes upfront in both functions before the stripping
loop, mirroring the pattern Utils.path_can_match_spec? already uses.

Spec coverage in spec/datadog/di/code_tracker_spec.rb covers:
- Windows-style probe path with prefix stripping required (the failing case)
- Windows-style + uppercase, exercising both backslash normalization and
  the case-insensitive fallback
- Absolute Windows-style path

Verified: 3 new specs pass; full code_tracker_spec/utils_spec/instrumenter_spec/
probe_spec suite (203 examples) passes; standardrb clean; steep clean.

Co-Authored-By: Claude <[email protected]>