feat(dynamic-sampling): add per-project volume query

[shellmayr]

• Add Query to EAP for per-project span volumes that will serve as the basis for the low-volume project calculations

Closes TET-2276

[linear-code]

TET-2276 Write query for project base sample rate calculations (boost low volume projects)

[sentry]

Bug: Calling int() on row["sentry.dsc.root_project"] will raise a TypeError when the value is None, which occurs for spans lacking a DSC header.
_{Severity: HIGH}

Suggested Fix

Add a null check before casting the sentry.dsc.root_project value to an integer. Handle the None case gracefully, for example by assigning a default value or skipping the row, similar to how _get_aggregate_int handles nulls.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/sentry/dynamic_sampling/per_org/tasks/queries.py#L146

Potential issue: The code directly accesses `row["sentry.dsc.root_project"]` and
attempts to cast it to an integer using `int()`. However, when processing spans that
lack a Dynamic Sampling Context (DSC) header, which is a realistic scenario with older
SDKs or incomplete trace propagation, the value for `sentry.dsc.root_project` can be
`None`. Attempting to execute `int(None)` will raise a `TypeError`, causing the task to
crash. While other parts of the code handle null values correctly, this specific access
point lacks the necessary null check.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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