Support session-time source configuration in DataFusion, and clear up precedence between config sources

[AdamGS]

Rational for this change

Makes it possible to configure Vortex FileSource-based tables using SET statements on an appropriately configured DataFusion session. This is mostly useful for testing or interactive workflows.

What changes are included in this PR?

1. Use DataFusion's ExtensionOptions and ConfigExtension APIs instead of config_namespace to get configuration handling for free.
2. Adds SLT based tests for table and session configuration.
3. Better document the order of precedence between the various sources of config, trying to mirror the built-in file formats.

What APIs are changed? Are there any user-facing changes?

For users of VortexSource and VortexFormat, some APIs might change slightly, and if they expose Vortex through an interactive interface, the config might change slightly.

[codspeed-hq]

Merging this PR will improve performance by 11.9%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 4 improved benchmarks
✅ 1585 untouched benchmarks
⏩ 4 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	encode_varbin[(1000, 4)]	157 µs	139.8 µs	+12.34%
⚡	Simulation	encode_varbin[(1000, 32)]	162.5 µs	144.8 µs	+12.22%
⚡	Simulation	encode_varbin[(1000, 8)]	157.3 µs	140.4 µs	+12.05%
⚡	Simulation	encode_varbin[(1000, 2)]	156.1 µs	140.7 µs	+10.98%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing adamg/support-settings-config-session (2ab0b57) with develop (2a19323)}

Footnotes

1. 4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩