Add: reserve parameter added to Index for c# sdk

[jamesryanbell]

Add reserve parameter to all USearchIndex constructors

This addresses #441

Summary

This PR adds an optional reserve parameter to all three USearchIndex constructors to allow pre-allocation of memory for incoming vectors, improving performance when the expected number of vectors is known in advance.

Changes Made

1. First Constructor (Parameter-based)

• Before:

  public USearchIndex(MetricKind metricKind, ScalarKind quantization, ulong dimensions, 
                      ulong connectivity = 0, ulong expansionAdd = 0, ulong expansionSearch = 0, 
                      bool multi = false)

• After:

  public USearchIndex(MetricKind metricKind, ScalarKind quantization, ulong dimensions, 
                      ulong connectivity = 0, ulong expansionAdd = 0, ulong expansionSearch = 0, 
                      bool multi = false, ulong reserve = 0)

2. Second Constructor (IndexOptions-based)

• Before:

  public USearchIndex(IndexOptions options)

• After:

  public USearchIndex(IndexOptions options, ulong reserve = 0)

• Added reserve logic: if (reserve > 0) { this.IncreaseCapacity(reserve); }
• Added XML documentation for the new parameter

3. Third Constructor (File-based)

• Before:

  public USearchIndex(string path, bool view = false)

• After:

  public USearchIndex(string path, bool view = false, ulong reserve = 0)

• Added reserve logic: if (reserve > 0) { this.IncreaseCapacity(reserve); }
• Added XML documentation for the new parameter

Benefits

• Performance: Pre-allocates memory to avoid reallocations during vector insertion
• Consistency: All constructors now support the same reserve functionality
• Backward Compatibility: Default value of 0 ensures existing code continues to work

Usage Examples

// Pre-allocate for 1000 vectors
var index1 = new USearchIndex(MetricKind.Cos, ScalarKind.Float32, 128, reserve: 1000);

// Pre-allocate when loading from file
var index2 = new USearchIndex("index.usearch", reserve: 5000);

// Pre-allocate with IndexOptions
var options = new IndexOptions { /* ... */ };
var index3 = new USearchIndex(options, reserve: 2000);

Breaking Changes

None - this is a purely additive change with default parameter values.

[jamesryanbell]

Hi @ashvardanian, do you know when someone will be able to review this please

[ashvardanian]

Hi @jamesryanbell! Thanks for the PR!

I don't yet see the relationship between the proposed APIs and multi-threading in #441.

Why do we need a reserve argument in multiple methods as opposed to a single reserve method?

[jamesryanbell]

Hi @ashvardanian, when I try and create an index using multiple threads I run into an issue where the capacity is not increased. This change would allow me to set the capacity before the parallel operation.

I can't resize increase the capacity currently as IncreaseCapacity is a private method