feat(context): expose determined bump type in release context

[ChihebBENCHEIKH1]

Closes #1220

Adds a bump_type field to the Release struct, exposing the determined version bump type in both templates and the JSON context output (-x).

Values: "major", "minor", "patch", or null

Usage in templates:
{% if bump_type == "major" %}Breaking release{% endif %}

In JSON context (--context):
{"version": "1.2.0", "bump_type": "minor", ...}

How it works:

• When bump_type is forced via config, uses that directly
• Otherwise, compares the previous and next semver versions to determine the type
• Returns null when no previous version exists (initial tag)

Changes:

• Added bump_type: Option<BumpType> to Release struct
• Modified calculate_next_version_with_config to return the determined bump type
• Updated bump_version() to populate the field
• Added bump_version_type test covering auto-detection, forced config, and initial tag cases

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.83%. Comparing base (ee8bfd1) to head (4e6abc8).

Files with missing lines	Patch %	Lines
git-cliff-core/src/release.rs	91.31%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1483      +/-   ##
==========================================
+ Coverage   47.40%   47.83%   +0.44%     
==========================================
  Files          24       24              
  Lines        2129     2141      +12     
==========================================
+ Hits         1009     1024      +15     
+ Misses       1120     1117       -3     

Flag	Coverage Δ
unit-tests	47.83% <92.00%> (+0.44%)	⬆️

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[ChihebBENCHEIKH1]

Nope, all done! The force pushes were just formatting fixes. CI is green now.