fix: Refined encoding logic for array of nested objects

[Vedant-03]

Description

This PR fixes the encoding logic for array of nested objects. The current implementation encodes the JSON [{"a": {"b": "123"}}] as

[1]:
  -
    a:
      b: "123"

The change fixes this to be encoded as

[1]:
  - a:
      b: "123"

I have refined the logic for encoding object as list item to put the first key in a nested object on same line with "-" and continue encoding its corresponding value further according to SPEC.md. The decoding logic already looks good and needed change. This PR also adds a test case to validate the case.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Related Issues

Closes #33

Changes Made

• Put the first key of nested object on the same line with "-", when encoding it as list item.
• Added a test case to validate encoding array of nested object(s).

SPEC Compliance

• This PR implements/fixes spec compliance
• Spec section(s) affected:
  • 10
• Spec version: 2.0

Testing

• All existing tests pass
• Added new tests for changes
• Tested on Python 3.8
• Tested on Python 3.9
• Tested on Python 3.10
• Tested on Python 3.11
• Tested on Python 3.12
• Tested on Python 3.13
• Tested on Python 3.14

Test Output

==================================================== tests coverage ===================================================== 
____________________________________ coverage: platform win32, python 3.14.0-final-0 ____________________________________ 

Name                                Stmts   Miss   Cover   Missing
------------------------------------------------------------------
src\toon_format\__init__.py             6      0 100.00%
src\toon_format\__main__.py             4      4   0.00%   8-13
src\toon_format\_literal_utils.py      13      1  92.31%   58
src\toon_format\_parsing_utils.py      44      0 100.00%
src\toon_format\_scanner.py            80      0 100.00%
src\toon_format\_string_utils.py       60      0 100.00%
src\toon_format\_validation.py         29      0 100.00%
src\toon_format\cli.py                 77      1  98.70%   217
src\toon_format\constants.py           30      0 100.00%
src\toon_format\decoder.py            338     28  91.72%   98-99, 135, 156-157, 172, 183, 204, 364-365, 412-414, 529, 539,src\toon_format\encoder.py             21      1  95.24%   54
src\toon_format\logging_config.py      31      8  74.19%   83-92
src\toon_format\normalize.py           92      5  94.57%   25, 108-109, 116-117
src\toon_format\types.py               18      0 100.00%
src\toon_format\utils.py               37     25  32.43%   44-48, 61-62, 85-91, 120-131, 166-187
src\toon_format\writer.py              18      0 100.00%
------------------------------------------------------------------
================================================ short test summary info ================================================ 
============================================ 794 passed, 13 skipped in 5.66s ============================================

Code Quality

• Ran ruff check src/toon_format tests - no issues
• Ran ruff format src/toon_format tests - code formatted
• Ran mypy src/toon_format - no critical errors
• All tests pass: pytest tests/ -v

Checklist

• My code follows the project's coding standards (PEP 8, line length 100)
• I have added type hints to new code
• I have added tests that prove my fix/feature works
• New and existing tests pass locally
• I have updated documentation (README.md, CLAUDE.md if needed)
• My changes do not introduce new dependencies
• I have maintained Python 3.8+ compatibility
• I have reviewed the TOON specification for relevant sections

Performance Impact

• No performance impact
• Performance improvement (describe below)
• Potential performance regression (describe and justify below)

Breaking Changes

• No breaking changes
• Breaking changes (describe migration path below)

Checklist for Reviewers

• Code changes are clear and well-documented
• Tests adequately cover the changes
• Documentation is updated
• No security concerns
• Follows TOON specification
• Backward compatible (or breaking changes are justified and documented)

[Justar96]

Thanks for the PR @Vedant-03