upgrade `extract_begin_end` function

[csae8092]

• process notBefore-iso and notAfter-iso="1889-12-31"
• provide param to decide if "when-iso" should be considered if also notBefore/notAfter exist

take following example:

<person xml:id="pmb2161">
  <persName>
      <forename>Emerich von</forename>
      <surname>Bukovics</surname>
  </persName>
  <persName type="person_geburtsname_nachname">Bukovics von Kiss-Alacsa</persName>
  <persName type="legacy-name-merge">Bukovics, Emerich von</persName>
  <birth>
    <date when-iso="1844-02-28">28.02.1844</date>
      <settlement key="pmb50">
        <placeName type="pref">Wien</placeName>
        <location><geo>48.2066 16.37341</geo></location>
      </settlement>
  </birth>  
  <death>
    <date when-iso="1905-07-04">04.07.1905</date>
      <settlement key="pmb50">
        <placeName type="pref">Wien</placeName>
        <location><geo>48.2066 16.37341</geo></location>
      </settlement>
  </death>
  <sex value="male"/>
  <occupation key="99">Journalist/Journalistin</occupation>
  <occupation key="103">Theaterleiter/Theaterleiterin</occupation>
  <idno type="URL" subtype="gnd">https://d-nb.info/gnd/11715380X</idno>
<affiliation notBefore-iso="1889-01-01" when-iso="1889-07-02" notAfter-iso="1889-12-31">
    <term key="1182">arbeitet für</term>
    <orgName key="pmb36430">Volkstheater</orgName>
    <idno type="URL" subtype="gnd">https://d-nb.info/gnd/146313-5</idno>
</affiliation>
<listEvent>
    <event key="35095" when-iso="1900-12-01">
        <desc n="1370">teilgenommen an</desc>
        <label>Uraufführung von Der Schleier der Beatrice, 1.12.1900</label>
        <idno type="URL" subtype="pmb">https://pmb.acdh.oeaw.ac.at/entity/35095</idno>
    </event>
    <event key="35272" when-iso="1904-02-13">
        <desc n="1370">teilgenommen an</desc>
        <label>Uraufführung von Der einsame Weg, 13.2.1904</label>
        <idno type="URL" subtype="pmb">https://pmb.acdh.oeaw.ac.at/entity/35272</idno>
    </event>
    <event key="93033" when-iso="1893-11-11">
        <desc n="1370">teilgenommen an</desc>
        <label>Uraufführung von Der erste seines Stammes, 11.11.1893</label>
        <idno type="URL" subtype="pmb">https://pmb.acdh.oeaw.ac.at/entity/93033/</idno>
    </event>
  </listEvent>
</person>