template evaluation: handle string templates only

[snejus]

What changed

• Template evaluation is now routed through a single string-based API: evaluate_fmt(...).
• Format values are treated as plain strings everywhere, instead of sometimes being strings and sometimes compiled Template objects.
• Template compilation and caching are centralized in beets.util.functemplate.get_template(...).

Architecture impact

• dbcore now owns one clear path for evaluating format strings.
• path_formats now carries tuple[str, str] values, which removes type branching in consumers.
• Callers in library, modify, and plugins now pass raw format strings and rely on the shared helper to compile/cache them.

Why this matters

• Removes conditional logic around 'string vs Template object' handling.
• Makes the formatting flow easier to follow and easier to maintain.
• Keeps behavior the same at a high level while simplifying the internal contract for template usage.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.51%. Comparing base (beff630) to head (10f49d1).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6737      +/-   ##
==========================================
- Coverage   74.54%   74.51%   -0.03%     
==========================================
  Files         162      162              
  Lines       20832    20820      -12     
  Branches     3298     3295       -3     
==========================================
- Hits        15529    15515      -14     
- Misses       4548     4549       +1     
- Partials      755      756       +1     

Files with missing lines	Coverage Δ
beets/dbcore/db.py	94.07% <100.00%> (-0.02%)	⬇️
beets/library/models.py	87.63% <100.00%> (-0.14%)	⬇️
beets/ui/commands/modify.py	93.84% <ø> (-0.19%)	⬇️
beets/util/functemplate.py	88.64% <100.00%> (+0.04%)	⬆️
beets/util/pathformats.py	100.00% <100.00%> (ø)
beetsplug/bench.py	26.82% <ø> (-1.75%)	⬇️
beetsplug/smartplaylist.py	87.96% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[Copilot]

Pull request overview

grug see PR make template eval go through one string path: evaluate_fmt(...). goal is less “string vs Template object” branching.

Changes:

• rename model templating API to string-only evaluate_fmt(fmt, for_path=...) and route eval through get_template(...) cache
• switch path_formats plumbing to carry raw format strings (no compiled Template objects)
• update callers (library/models, modify command, smartplaylist, bench, tests) to pass strings

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/test_library.py	switch item template eval assertions to evaluate_fmt
test/plugins/test_types_plugin.py	switch template conditionals tests to evaluate_fmt
test/plugins/test_smartplaylist.py	update smartplaylist mocks to evaluate_fmt (but currently broken w/ kwargs + bytes)
test/plugins/test_rewrite.py	switch album template eval assertion to evaluate_fmt
test/plugins/test_inline.py	switch inline plugin test to evaluate_fmt
beetsplug/smartplaylist.py	use evaluate_fmt(..., for_path=True) for playlist name + debug formatting
beetsplug/bench.py	set lib.path_formats entries to raw format strings
beets/util/pathformats.py	make get_path_formats return (key, fmt_str) pairs
beets/util/functemplate.py	centralize compilation/cache under get_template(fmt)
beets/ui/commands/modify.py	remove per-run template compile dict; call evaluate_fmt directly
beets/library/models.py	switch formatting and path destination building to evaluate_fmt
beets/dbcore/db.py	replace evaluate_template with evaluate_fmt using get_template