refactor: enhance Filter and related structs

[xushiyan]

Description

• Rename PartitionFilter to SchemableFilter for generic use
• Fix missing Operator::NotEq support
• Add ergonomic functions for composing Filters, such as col("foo").eq("a")

Closes #160

Follow up #203

How are the changes test-covered

• N/A
• Automated tests (unit and/or integration tests)
• Manual tests
  • Details are described below

[codecov]

Codecov Report

Attention: Patch coverage is 95.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.32%. Comparing base (eb0f520) to head (92857dc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/expr/filter.rs	95.45%	2 Missing ⚠️
crates/datafusion/src/util/expr.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #221      +/-   ##
==========================================
- Coverage   91.34%   91.32%   -0.02%     
==========================================
  Files          24       24              
  Lines        1074     1095      +21     
==========================================
+ Hits          981     1000      +19     
- Misses         93       95       +2     

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