[BUG] seeded fn:random-number-generator must be consistent within a single execution context

[line-o]

Describe the bug

For a vast range of seeds the randomness is not consistent within a single execution context.

• any string not castable as xs:integer
• any date, dateTime
• any xs:decimal not castable as xs:integer
• xs:integer larger than 9223372036854775807

fn:random-number-generator("a")?number eq
fn:random-number-generator("a")?number

is false()

Expected behavior

The xquery 3.1 specification clearly states that the result of fn:random-number-generator("a")?number must be the same within the same execution context.

Both forms of the function are ·deterministic·: calling the function twice with the same arguments, within a single ·execution scope·, produces the same results.

https://www.w3.org/TR/xpath-functions/#func-random-number-generator

related feature request #3912 might be implemented with a fix for this issue

To Reproduce

xquery version "3.1";

module namespace t="http://exist-db.org/xquery/test";

declare namespace test="http://exist-db.org/xquery/xqsuite";

declare
    %test:assertTrue
function t:test() {
  fn:random-number-generator("a")?number eq
  fn:random-number-generator("a")?number
};

Context (please always complete the following information):

• OS: macOS 10.15.7
• eXist-db version: 5.3.0-SNAPSHOT
• Java Version Java8 1.8.0_252-b09

Additional context

• How is eXist-db installed? built from source
• Any custom changes in e.g. conf.xml? none