Fix three statements that could cause problems on Windows

[martinholmer]

These changes have no effect on non-Windows platforms: all the tests pass and the three generated national TMD data files are the same as before these changes.

Commit f20d1f1 fixes this issue:

  A temp-file reopened while open (fails on Windows)

  tests/test_solve_weights.py:172-177
  with tempfile.NamedTemporaryFile(mode="w", suffix=".log", delete=False) as f:
      f.write(log_content)
      f.flush()
      result = parse_log(Path(f.name))   # reopens f.name while f is still open

  On Linux/macOS a file can be opened by a second handle while the first is
  open. On Windows the file is locked, so parse_log()'s open() raises
  PermissionError. The fix is to close the temp file before reopening — move the
  parse_log call outside the with block.

Commit 0ec32bc fixes this issue:

  Console-encoding crash on Windows — non-ASCII in print()

  tmd/national_targets/extract_irs_to_csv.py:230 and
  tmd/national_targets/potential_targets_to_soi.py:436 both print() a →
  (U+2192).

  On Windows, when stdout is redirected to a file or pipe, Python encodes using
  the locale code page (cp1252), which has no → → UnicodeEncodeError. (Other
  non-ASCII output like —, ±, × is in cp1252, so those are safe; →, ←, Σ, ✓ are
  not.) Note the log files written with explicit encoding="utf-8" and the
  io.StringIO capture in batch_weights.py are all safe — only direct console
  prints are at risk.

[martinholmer]

@donboyd5 approved this PR in a private email.