feat: matrix testing for python 3.14

[matmair]

Adds a CI step and 3.14 optimized requirement export for python 3.14 to ensure upstream compatibility (3.14 is the first free-thread version).

[netlify]

✅ Deploy Preview for inventree-web-pui-preview canceled.

Name	Link
🔨 Latest commit	a3300a7
🔍 Latest deploy log	https://app.netlify.com/projects/inventree-web-pui-preview/deploys/696ece1f4e85fa000845d0dd

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.02%. Comparing base (6311f75) to head (2e04e94).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10904      +/-   ##
==========================================
- Coverage   88.17%   87.02%   -1.15%     
==========================================
  Files        1290     1290              
  Lines       58223    58223              
  Branches     1968     1968              
==========================================
- Hits        51336    50667     -669     
- Misses       6396     7065     +669     
  Partials      491      491              

Flag	Coverage Δ
backend	89.48% <ø> (+0.01%)	⬆️

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Components	Coverage Δ
Backend Apps	90.17% <ø> (-1.85%)	⬇️
Backend General	93.16% <ø> (-0.33%)	⬇️
Frontend	70.83% <ø> (ø)

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[matmair]

DO NOT MERGE; removes security feature