[r] Extend iterated reader interface with platform_config

[eddelbuettel]

This PR extend the 'iterating reader' to accept an optional argument config: a (standard R) named character vector for key=value pairs used to seed the platform_config map. This now permits to set configuration values. Here is an example of turning logging one by passing config=c("config.logging_level" = "5"):

$ ./quickCheck.R 
[2022-11-18 17:24:38.034] [Process: 2773728] [info] [1668813877360419015-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:24:38.274] [Process: 2773728] [info] [1668813877360419015-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:24:38.355] [Process: 2773728] [info] [1668813877360419015-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:24:38.543] [Process: 2773728] [info] [1668813877360419015-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:24:38.543] [Process: 2773728] [info] [1668813877360419015-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:24:38.765] [Process: 2773728] [trace] [1668813878010788925-Global] malloc_trim did unmap memory
$ 

We can combine this with the existing logging support from R which, when set to debug, also shows the value being set (see second line):

$ ./quickCheck.R 
[2022-11-18 17:49:39.119] [default] [Process: 2837302] [info] [sr_setup] Setting up ~/git/tiledb-soma/test/soco/pbmc3k_processed/ms/mRNA/X/data/
[2022-11-18 17:49:39.119] [default] [Process: 2837302] [debug] [sr_setup] config map adding 'config.logging_level' = '5'
[2022-11-18 17:49:39.119] [default] [Process: 2837302] [debug] [sr_setup] creating ctx object with supplied config
[2022-11-18 17:49:39.122] [default] [Process: 2837302] [info] [soma_reader] Dimension soma_dim_0 type INT64 domain [0,2637] extent 2048
[2022-11-18 17:49:39.122] [default] [Process: 2837302] [info] [soma_reader] Dimension soma_dim_1 type INT64 domain [0,1837] extent 1838
[2022-11-18 17:49:39.137] [Process: 2837302] [info] [1668815378482964946-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:49:39.186] [default] [Process: 2837302] [info] [sr_complete] Complete test is false
[2022-11-18 17:49:39.186] [default] [Process: 2837302] [info] [sr_next] Read 1213080 rows and 3 cols
[2022-11-18 17:49:39.354] [default] [Process: 2837302] [info] [sr_complete] Complete test is false
[2022-11-18 17:49:39.365] [Process: 2837302] [info] [1668815378482964946-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:49:39.403] [default] [Process: 2837302] [info] [sr_next] Read 1211242 rows and 3 cols
[2022-11-18 17:49:39.436] [default] [Process: 2837302] [info] [sr_complete] Complete test is false
[2022-11-18 17:49:39.449] [Process: 2837302] [info] [1668815378482964946-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:49:39.493] [default] [Process: 2837302] [info] [sr_next] Read 1213080 rows and 3 cols
[2022-11-18 17:49:39.618] [default] [Process: 2837302] [info] [sr_complete] Complete test is false
[2022-11-18 17:49:39.633] [Process: 2837302] [info] [1668815378482964946-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:49:39.633] [Process: 2837302] [info] [1668815378482964946-Context: 2] [Query: 1] [DenseReader: 1] using cache
[2022-11-18 17:49:39.681] [default] [Process: 2837302] [info] [sr_next] Read 1211242 rows and 3 cols
[2022-11-18 17:49:39.835] [default] [Process: 2837302] [info] [sr_complete] Complete test is true
[2022-11-18 17:49:39.838] [Process: 2837302] [trace] [1668815379114681381-Global] malloc_trim did unmap memory
$ 

No other code change. No test added as there is currently no way to return a config so hard to check that values are set. We can address this later, as we can extending the other (simpler) SOMAReader interface.

I had accidentally pushed this same commit to main a few minutes ago, but have undo that as main should only change after reviews of pull requests.

[shortcut-integration]

This pull request has been linked to Shortcut Story #23591: Expose platform config for iterated reader.