Closes #3998

Closes #3998

`continue_trace` now propagates incoming `sample_rand` values to the transaction's baggage. Also, in the case where `sample_rand` is missing from the incoming trace and needs to be backfilled, this change introduces a mechanism for the backfilled value from the scope's propagation context to be propagated to the transaction's baggage.

The transaction still does not use the `sample_rand` for making sampling decisions; this PR only enables propagation. A future PR will add support for reading the incoming/backfilled `sample_rand` and for using this value to make sampling decisions.

Ref #3998

Whenever the `PropagationContext` continues an incoming trace (i.e. whenever the `trace_id` is set, rather than being randomly generated as for a new trace), check if the `sample_rand` is present and valid in the incoming DSC. If the `sample_rand` is missing, generate it deterministically based on the `trace_id` and backfill it into the DSC on the `PropagationContext`.

When generating the backfilled `sample_rand`, we ensure the generated value is consistent with the incoming trace's sampling decision and sample rate, if both of these are present. Otherwise, we generate a new value in the range [0, 1).

Future PRs will address propagating the `sample_rand` to transactions generated with `continue_trace` (allowing the `sample_rand` to be propagated on outgoing traces), and will also allow `sample_rand` to be used for making sampling decisions.

Ref #3998

`continue_trace` now propagates incoming `sample_rand` values to the transaction's baggage. Also, in the case where `sample_rand` is missing from the incoming trace and needs to be backfilled, this change introduces a mechanism for the backfilled value from the scope's propagation context to be propagated to the transaction's baggage.

The transaction still does not use the `sample_rand` for making sampling decisions; this PR only enables propagation. A future PR will add support for reading the incoming/backfilled `sample_rand` and for using this value to make sampling decisions.

Ref #3998

Whenever the `PropagationContext` continues an incoming trace (i.e. whenever the `trace_id` is set, rather than being randomly generated as for a new trace), check if the `sample_rand` is present and valid in the incoming DSC. If the `sample_rand` is missing, generate it deterministically based on the `trace_id` and backfill it into the DSC on the `PropagationContext`.

When generating the backfilled `sample_rand`, we ensure the generated value is consistent with the incoming trace's sampling decision and sample rate, if both of these are present. Otherwise, we generate a new value in the range [0, 1).

Future PRs will address propagating the `sample_rand` to transactions generated with `continue_trace` (allowing the `sample_rand` to be propagated on outgoing traces), and will also allow `sample_rand` to be used for making sampling decisions.

Ref #3998

`continue_trace` now propagates incoming `sample_rand` values to the transaction's baggage. Also, in the case where `sample_rand` is missing from the incoming trace and needs to be backfilled, this change introduces a mechanism for the backfilled value from the scope's propagation context to be propagated to the transaction's baggage.

The transaction still does not use the `sample_rand` for making sampling decisions; this PR only enables propagation. A future PR will add support for reading the incoming/backfilled `sample_rand` and for using this value to make sampling decisions.

Ref #3998

Whenever the `PropagationContext` continues an incoming trace (i.e. whenever the `trace_id` is set, rather than being randomly generated as for a new trace), check if the `sample_rand` is present and valid in the incoming DSC. If the `sample_rand` is missing, generate it deterministically based on the `trace_id` and backfill it into the DSC on the `PropagationContext`.

When generating the backfilled `sample_rand`, we ensure the generated value is consistent with the incoming trace's sampling decision and sample rate, if both of these are present. Otherwise, we generate a new value in the range [0, 1).

Future PRs will address propagating the `sample_rand` to transactions generated with `continue_trace` (allowing the `sample_rand` to be propagated on outgoing traces), and will also allow `sample_rand` to be used for making sampling decisions.

Ref #3998

`continue_trace` now propagates incoming `sample_rand` values to the transaction's baggage. Also, in the case where `sample_rand` is missing from the incoming trace and needs to be backfilled, this change introduces a mechanism for the backfilled value from the scope's propagation context to be propagated to the transaction's baggage.

The transaction still does not use the `sample_rand` for making sampling decisions; this PR only enables propagation. A future PR will add support for reading the incoming/backfilled `sample_rand` and for using this value to make sampling decisions.

Ref #3998

`continue_trace` now propagates incoming `sample_rand` values to the transaction's baggage. Also, in the case where `sample_rand` is missing from the incoming trace and needs to be backfilled, this change introduces a mechanism for the backfilled value from the scope's propagation context to be propagated to the transaction's baggage.

The transaction still does not use the `sample_rand` for making sampling decisions; this PR only enables propagation. A future PR will add support for reading the incoming/backfilled `sample_rand` and for using this value to make sampling decisions.

Ref #3998