file.kdb: Re-write getLength to add support for "new-format" lists

[jasraj]

• Also support atomic files
• Add getType for similar performance improvement (for large files)

[jasraj]

Related to [#61], performance comparison of lists each with 10 million elements:

• Single-typed lists (18 total, 1 per type)
• Anymap lists - list of character lists and list of multiple-type lists

.file.kdb.getType

Method	Uncompressed	Compressed (lz4hc)
.file.kdb.getType each x	1 9232	2 675376
type each get each x	398 138412688	450 143132240

.file.kdb.getLength

Method	Uncompressed	Compressed (lz4hc)
.file.kdb.getLength each x	1 9264	2 675376
count each get each x	393 138412688	456 143132240

Code

q) { set[`$":/tmp/kdb-types/",x; 10000000?y] }./: flip (key;value)@\:enlist[" "] _ .rand.charTypes;
q) set[`$":/tmp/kdb-types/str-anymap"; 10000000?.Q.a cross .Q.a];
q) set[`$":/tmp/kdb-types/num-anymap"; 10000000?(1 2 3; 1 2 3f; 1 2 3h)];

q) { set[(`$":/tmp/kdb-types-comp/",x),.compress.defaults`lz4hc; 10000000?y] }./: flip (key;value)@\:enlist[" "] _ .rand.charTypes;
q) set[(`$":/tmp/kdb-types-comp/str-anymap"),.compress.defaults`lz4hc; 10000000?.Q.a cross .Q.a];
q) set[(`$":/tmp/kdb-types-comp/num-anymap"),.compress.defaults`lz4hc; 10000000?(1 2 3; 1 2 3f; 1 2 3h)];

q) srcs:.file.listFolderPaths `$":/tmp/kdb-types";
q) srcs@:where not srcs like "*#";
q) compSrcs:.file.listFolderPaths `$":/tmp/kdb-types-comp";
q) compSrcs@:where not compSrcs like "*#";

q) (.file.kdb.getType each srcs) = type each get each srcs
11111111111111111111b
q) (.file.kdb.getType each compSrcs) = type each get each compSrcs
11111111111111111111b
q) (.file.kdb.getLength each srcs) = count each get each srcs
11111111111111111111b
q) (.file.kdb.getLength each compSrcs) = count each get each compSrcs
11111111111111111111b

[jasraj]

For splayed tables, using .Q.V results in identical performance to the .file.kdb.get* functions:

q) get `:/tmp/hdb/2021.11.08/trade
time                          sym  price    vol    prices
--------------------------------------------------------------
2015.01.04D04:55:29.310114176 22   34.61037 744631 100 101 102
...

q) \ts type each .Q.V `:/tmp/hdb/2021.11.08/trade
1 4195152
q) \ts .file.kdb.getType each ` sv/: `:/tmp/hdb/2021.11.08/trade,/: cols `:/tmp/hdb/2021.11.08/trade
1 4195664

q) \ts count each .Q.V `:/tmp/hdb/2021.11.08/trade
1 4195152
q) \ts .file.kdb.getLength each ` sv/: `:/tmp/hdb/2021.11.08/trade,/: cols `:/tmp/hdb/2021.11.08/trade
1 4195664