feat: initial rule engine + memo table

[AlSchlo]

Problem

The persistent memo layer and the rule engine are the core components that facilitate query plan transformation.

Having an initial setup is important for people to work on the same codebase simultaneously.

Summary of changes

• A memo table implementation backed by SQLite.
• Low-level IR for the rule engine proof concept.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.65391% with 368 lines in your changes missing coverage. Please review.

Project coverage is 70.6%. Comparing base (3962965) to head (758671f).

Files with missing lines	Patch %	Lines
optd-core/src/storage/memo.rs	81.9%	91 Missing ⚠️
optd-core/src/operators/relational/physical/mod.rs	0.0%	76 Missing ⚠️
...-core/src/engine/interpreter/expressions/values.rs	75.7%	32 Missing ⚠️
...c/operators/relational/physical/join/merge_join.rs	0.0%	26 Missing ⚠️
...rc/operators/relational/physical/join/hash_join.rs	0.0%	21 Missing ⚠️
...d-core/src/engine/interpreter/expressions/plans.rs	0.0%	18 Missing ⚠️
...ators/relational/physical/join/nested_loop_join.rs	0.0%	16 Missing ⚠️
optd-core/src/operators/scalar/mod.rs	69.5%	14 Missing ⚠️
optd-core/src/operators/relational/logical/mod.rs	78.5%	12 Missing ⚠️
...c/operators/relational/physical/scan/table_scan.rs	0.0%	12 Missing ⚠️
... and 10 more

Additional details and impacted files

Files with missing lines	Coverage Δ
optd-core/src/test_utils.rs	100.0% <100.0%> (ø)
optd-core/src/cascades/mod.rs	99.2% <99.2%> (ø)
optd-core/src/operators/scalar/add.rs	50.0% <50.0%> (ø)
optd-core/src/operators/scalar/column_ref.rs	62.5% <62.5%> (ø)
optd-core/src/operators/scalar/constants.rs	50.0% <50.0%> (ø)
optd-core/src/operators/scalar/equal.rs	50.0% <50.0%> (ø)
...td-core/src/operators/relational/logical/filter.rs	33.3% <33.3%> (ø)
optd-core/src/operators/relational/logical/scan.rs	50.0% <50.0%> (ø)
optd-core/src/operators/relational/logical/join.rs	50.0% <50.0%> (ø)
optd-core/src/storage/transaction.rs	91.5% <91.5%> (ø)
... and 11 more