Log attribute-discard messages at most once per `LogRecord` (both truncation paths)

Spec requirement

There SHOULD be a message printed in the SDK's log to indicate an attribute was discarded due to a limit; to prevent excessive logging, the message MUST be printed at most once per LogRecord, not per discarded attribute (sdk.md:354-357 (permalink)).

Current behavior

logs_sdk/lib/opentelemetry/sdk/logs/log_record.rb:138-141 (permalink) (truncate_attributes, the attribute-count-limit path) drops excess attributes via attributes.shift with no logging call.

:143-159 (permalink) (validate_attributes, the type-validity path) calls OpenTelemetry.handle_error once per invalid attribute inside a keep_if block, so a record with 3 bad attributes logs 3 separate messages, causing too many messages to be logged.

Suggested fix

Add a single summarizing discard-logging call to truncate_attributes, and collect invalid-attribute violations in validate_attributes into one summary message per LogRecord instead of one handle_error call per attribute.

Related rows in SPEC_COMPLIANCE_LOGS.md

SDK-31

Start with logs_sdk/lib/opentelemetry/sdk/logs/log_record.rb, reading truncate_attributes and validate_attributes alongside sdk.md:354-357. Verify both attribute-discard paths and the existing OpenTelemetry.handle_error behavior. Done means each LogRecord produces at most one summarizing discard message, including when both truncation paths are involved.