Add Database Reco Counts report client support

[adamtheturtle]

Summary

Add client support for the Database Reco Counts report, the last VWS endpoint with no vws-python equivalent.

Real Vuforia exposes POST /imagetargets/databases/{database_id}/reports/recoCounts, which asks for a per-target recognition-count report for a month and returns a presigned URL. The URL serves a CSV with a target_id,reco_count header once the report has been generated, and 404s until then.

vws-python-mock implements both halves of this as of VWS-Python/vws-python-mock#3357, including database ID validation, month validation and the generation delay, so a client can be tested end to end through a real HTTP transport.

What the endpoint does

• The request body is {"month": "YYYY-mm"}. Only the current month and the previous month are accepted; anything else gets a 400 with the Fail result code.
• The success body has result_code, transaction_id and presigned_url.
• The database_id in the path must be the ID of the database the server keys belong to. Naming any other database — including naming the database by its name rather than its ID — gets a 401 with AuthenticationFailure.
• The download URL needs no authorization headers. It returns 404 while the report is still being generated and 200 with text/plain (not text/csv) once it is ready. Rows end with CRLF.
• Real presigned URLs expire after just under seven days.

Why this needs more than a new method

VWS is constructed with a server access key and a server secret key only. This endpoint is the first to need the database ID, which is not derivable from the keys and is not returned by any other VWS endpoint — the target manager shows it, and vws-web-tools exposes it via get_database_details. So either VWS.__init__ grows an optional database_id, or the report method takes one. An optional constructor argument that raises a clear error when the method is called without it seems the better fit, but the trade-off is worth deciding explicitly.

The download is also unlike every other call in the library: it is unsigned, it is not against base_vws_url, and its "not ready yet" state is a 404 rather than a result code. It should not go through make_request.

Suggested scope

• Add a get_database_reco_counts_report-style method to VWS and AsyncVWS which requests the report and returns the presigned URL alongside the transaction ID.
• Add a way to download a report from its URL, without signing, exposing "not ready" distinctly from an error.
• Add a wait/poll helper in the style of wait_for_target_processed.
• Parse the CSV into a typed report structure in reports.py — a sequence of target ID and count pairs — rather than handing back raw bytes. Keeping a raw-bytes accessor as well is worth considering, since the CSV shape is not documented by Vuforia and could gain columns.
• Map the failure responses onto the existing exception types, including the Fail for a bad month and the AuthenticationFailure for a mismatched database ID.
• Document the month restriction, the URL expiry and the delay before the report is ready.

Acceptance criteria

• Synchronous and asynchronous APIs cover request → wait → download → parse.
• Tests exercise both clients against vws-python-mock, covering a successful report, a download attempted before the report is ready, a rejected month, and a mismatched database ID.
• A report for a database with no recognitions parses as an empty sequence of rows rather than failing.
• API reference documentation, an example, and a news fragment are included.

Notes

The mock's coverage of this endpoint is not verified against real Vuforia yet: the shared test credentials carry no database ID, so the tests are mock-only (VWS-Python/vws-python-mock#3359, VWS-Python/vws-python-mock#3360). The presigned URL's name, query parameters and expiry differ from real Vuforia (VWS-Python/vws-python-mock#3364), and the mock's reports are always header-only until VWS-Python/vws-python-mock#3356 lands. Client tests should avoid depending on the URL's shape, and cannot yet assert on non-empty report bodies.