Fix/launch template unsafe quoting, and performance improvements

[tcutts]

Fix unsafe shell variable expansions and quoting in launcher scripts

All launcher scripts (aprun_launch.sh, jsrun_launch.sh, mpi_launch.sh, multi_launch.sh, single_launch.sh, srun_launch.sh) and the test launcher.sh had several quoting issues that would cause failures when paths contain spaces. This PR fixes them all:

1. Replaced source $(dirname "$0")/launcher_lib.sh with source "${0%/*}/launcher_lib.sh" in all scripts, using shell parameter expansion to avoid both the unquoted command substitution and the nested quoting problem that would result from quoting it.
2. Quoted all uses of $_PSI_J_STDOUT, $_PSI_J_STDERR, $_PSI_J_STDIN, $_PSI_J_PROCESS_COUNT, and $_PSI_J_EC in redirections and command arguments throughout all scripts.

In launcher_lib.sh:

1. Added a _psi_j_abspath() helper that resolves all incoming path arguments to absolute paths at startup, preventing misresolution if the working directory changes during execution.
2. Replaced backtick command substitution in ts() with $(...).
3. On bash 4.2+, ts() now uses printf '%(%Y-%m-%d %H:%M:%S)T' — a zero-fork builtin — instead of spawning a date subprocess for every line of output. The original date-based implementation is retained as a fallback for older bash.

For 10,000 lines of output this saves about 18 seconds of execution time (benchmarked on an M1 Macbook)

[hategan]

Thank you @tcutts!

I'll copy the PR to our repo to let our distributed tests run and merge this once that happens.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.01%. Comparing base (de87be0) to head (03a249d).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #542      +/-   ##
==========================================
+ Coverage   72.80%   75.01%   +2.20%     
==========================================
  Files          89       91       +2     
  Lines        4012     4567     +555     
==========================================
+ Hits         2921     3426     +505     
- Misses       1091     1141      +50     

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