Feature patch: Reduce mythfilldatabase channel insert time (after #12685)

[Gary Buhrmaster <gary.buhrmaster@…>]

Feature patch: Reduce mythfilldatabase channel insert time (after #12685)

While DOing the TODO in #12685 (detect a CableCARD in Ceton devices) is arguably the right thing to do, a side effect is that the initial channel insert for a Ceton device may take substantial time to complete (apparently the web server for a Ceton device may take 2-3 seconds to complete the transaction to query the CableCARD status, and for a (typical) 500 channel map on a cable system, that can mean delays of around 20 minutes during an initial mythfilldatabase run (the delays would likely be small in subsequent runs as there are few/no channel inserts).

As consumer devices do not normally support CableCARD OIR, this patch determines the tuner unscannability once, and uses it for each channel to be inserted (if any).

Initial insert time for a Ceton device is now in seconds rather than 20 minutes (the improvement for a SiliconDust? device is likely far less, as their devices uses a different (and much faster) process, but less network traffic is always better).

github ref: ​https://github.com/garybuhrmaster/mythtv/commit/8f91f779b11e4f89efab8cc5b791aa6ada8568be

gitbug git-am ref: ​https://github.com/garybuhrmaster/mythtv/commit/8f91f779b11e4f89efab8cc5b791aa6ada8568be.patch

[Gary Buhrmaster <gary.buhrmaster@…>]

In e9c9cb1d3e2cd094a5152f1f7390a90748189e43/mythtv:

mythfilldatabase: Evaluate unscannable source status once

For some OCUR tuners (i.e. the Ceton), requesting
the status of whether the tuner has an inserted
CableCARD can take 2-3 seconds. Repeatedly
making that determination at each channel insert
time can result in slow channel update times if
the channel list is large. Determine the status
only once for the tuner.

Fixes #12756

Signed-off-by: Peter Bennett <pbennett@…>