Add custom comparison support for dbt-jinja objects

[boezzz]

refs #583

This PR introduces custom_cmp method to the Object trait. ALL the core logic (except datatime.rs) is directly copied from minijinja repo minijinja/pull/707.
Please also refer to this issue in minijinja repo for more details: mitsuhiko/minijinja#703

Changes:

• Added custom_cmp to the Object trait

• Integrated runtime type checking using TypeId to ensure custom_cmp is only called for objects of the matching type (Note: will cause undefined behavior when comparing objects of different types)

• Implemented timestamp-based comparison for PyDateTime objects as an example

• Added comprehensive tests for datetime comparison

⚠️ Known Limitation:
Comparing two different types fall back to default comparison logic and may trigger undefined bahavior. Previously, comparisons between different but related types (e.g., datetime vs. date) may return incorrect results due to a fallback to Maps comparison. modules.datetime.datetime(2025, 1, 1, 12, 0, 0)==modules.datetime.date(2025, 1, 1) would return true. This was because Both types used the default repr() implementation which returns ObjectRepr::Map. And when compared as maps with empty enumerators, the comparison logic would iterate over zero items and return true.

To address the issue above without breaking changes, we can explicitly implement repr() for custom types to return ObjectRepr::Plain.

In future PRs:

• landing pads for Python sort violations: Implemented landing pads for Python sort violations mitsuhiko/minijinja#713
• custom comparison for datetime.date and other object types

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[felipecrv]

Too many terrible fallbacks that would become a nightmare if we started depending on. This is how languages (minijina is a programming language implementation) end up with really bad semantics. Allocating on comparisons and falling back to string comparisons is not OK.

We should think about a different solution to the specific problems on a case-by-case basis.

[felipecrv]

Oh my. Just noticed it's an upstream change. 😓