fix: Escape attribute names reported in redactedAttributes

[kinyoklion]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Surfaced by contract test harness v3.2.0-alpha.6 (the pin bump in #414). These 6 subtests failed against the newer harness:

• events/context properties/single-kind, allAttributesPrivate, slash-prefixed attribute name (debug, identify, index-from-evaluation, index-from-custom-event)
• events/feature events/single-kind anonymous context redacts all attributes/type: any
• events/feature events/multi-kind with anonymous context redacts attributes appropriately/type: any

Describe the solution you've provided

_meta.redactedAttributes in event payloads is a list of attribute references, not raw attribute names. When a context has an attribute whose name begins with / (e.g. /ssn), the SDK emitted the raw name, which a consumer parses as a path expression pointing at a nested property rather than the top-level attribute:

expected: "/~1ssn"
actual:   "/ssn"

ContextFilter#check_whole_attribute_private now converts the attribute name to a reference with Reference.create_literal before adding it to the redacted list, which escapes / and ~ for slash-prefixed names and leaves all other names unchanged (name stays name, a/b~c stays a/b~c since it is already a literal reference). This covers both the allAttributesPrivate/configured-private paths and the anonymous-context redaction path, which is why one change fixes all 6 subtests.

Verified locally: contract test service against released harness v3.2.0-alpha.6, full suite — 4723 total, 14 skipped, all ran passed.

Describe alternatives you've considered

Escaping only in the all_attributes_private branch — rejected, the same escaping is required wherever a whole attribute is redacted.

Additional context

Nested redactions (redact_json_value) already reported Reference#raw_path, so they were unaffected.

Link to Devin session: https://app.devin.ai/sessions/316afaccd2604f8d802a72c9080f6921
Requested by: @kinyoklion

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