gnucash stable: [gnc-date.cpp] specialise iso-8601 parsing where TZ=+0000

[Christopher Lam]

Updated	 via  https://github.com/Gnucash/gnucash/commit/cba7da30 (commit)
	from  https://github.com/Gnucash/gnucash/commit/27c16517 (commit)



commit cba7da30fdae045d61ed04bdfd1c7abdac942a47
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Tue Mar 12 21:32:16 2024 +0800

    [gnc-date.cpp] specialise iso-8601 parsing where TZ=+0000
    
    - avoid allocating new TZPtr
    - parse y/m/d/h/m/s and construct PTime directly
    - avoid boost's time_from_string which creates an std::string



Summary of changes:
 libgnucash/engine/gnc-datetime.cpp | 66 ++++++++++++++++++++++++++++++++++----
 libgnucash/engine/gnc-datetime.hpp |  3 +-
 2 files changed, 62 insertions(+), 7 deletions(-)