Dunedin Symphony Orchestra principal second violin Ngaruaroha Martin is an expert at juggling contrasting worlds — the world of music and the world of construction. And now she is juggling caring for her 10-month-old son, Hono-Dean Smiler, with plenty of violin practice in the lead-up to Friday’s extraordinary Mahler’s Resurrection concert at Dunedin Town Hall. For the first time in more than 50 years, the Dunedin Symphony Orchestra and New Zealand Symphony Orchestra will join forces in concert, as they perform Mahler’s Symphony No 2 "Resurrection" along with up to 150 singers led by City Choir Dunedin and soloists Anna Leese (soprano) and Deborah Humbler (mezzo-soprano). The only other occasion the two orchestras have come together was for a Schola Cantorum concert in 1973 when the Civic Orchestra (the former name of the DSO) was augmented by members of the NZSO.…