Update read_cpi() to pull from the quarterly CPI (Table 17)

[justinduytran]

Since the December 2025 release, the ABS has changed the CPI series to make the monthly series Table 1. However the monthly series only dates back to April 2024 (compared to 1948 for the quarterly). This PR redirects the read_cpi() function to continue to read from the quarterly series instead of the monthly.

This does open a question about the intended purpose of the read_cpi() function.

1. Continuing to pull from the monthly CPI table (table 1) would be most simple.
2. Pulling from the quarterly series would arguably be more useful given the longer time horizon (and consistent with previous scripts that use the function).
3. Alternatively an argument could be created to handle both cases depending on user preference.

Further, the function could be rebuilt using read_api("CPI") (instead of read_abs()) and:

1. Have the option for both monthly, quarterly, or joining them together.
2. Arguments for which region's CPI.
3. Arguments for which analytical series (original, trend, seasonally adjusted).
4. It could even be extended beyond 'All groups CPI' and allow selection of groups/subgroups/classes or even measures (% change (YoY/MoM/QoQ), index, etc). But that might be too complex.

The above could all be done through read_abs() but would be less elegant...However it would have the benefit of being backwards compatible. read_api() would render many of the current arguments of read_cpi() (path, show progress bars, check_local, retain_files), obsolete.

Happy to go with whichever you prefer and I can amend the PR accordingly.