Enhance rustdocs with examples, module overviews, and cross-references

[Copilot]

Improves documentation coverage and quality across the workspace by adding practical examples, module-level context, and intra-doc links to aid discoverability.

Changes

Module-level documentation

• psbt/map: Explains PSBT key-value map structure and serialization format
• taproot/merkle_branch: Describes Merkle branch usage in Taproot script paths
• bip158: Adds BIP-0158 context for compact block filters
• crypto: Lists supported cryptographic operations
• network: Shows network type usage patterns

Function examples

Added runnable examples to commonly-used APIs:

• Sighash functions: TapSighashType::from_consensus_u8(), EcdsaSighashType::from_consensus(), ScriptPath constructors
• Script utilities: p2wpkh_script_code(), read_scriptint_non_minimal(), read_scriptbool()
• Taproot builders: with_huffman_tree(), add_leaf()

Complex type documentation

• Prevouts enum: Clarifies when to use One vs All variants with SIGHASH_ANYONECANPAY
• TaprootBuilder: Shows Huffman tree construction with weighted scripts
• PSBT Input: Demonstrates setting up inputs for SegWit transactions

Example

Before:

/// Constructs a new [`TapSighashType`] from a raw `u8`.
pub fn from_consensus_u8(sighash_type: u8) -> Result<Self, InvalidSighashTypeError>

After:

/// Constructs a new [`TapSighashType`] from a raw `u8`.
///
/// # Examples
///
/// ```
/// # use bitcoin::TapSighashType;
/// let sighash = TapSighashType::from_consensus_u8(0x00).expect("valid sighash");
/// assert_eq!(sighash, TapSighashType::Default);
/// ```
pub fn from_consensus_u8(sighash_type: u8) -> Result<Self, InvalidSighashTypeError>

All doctests pass. No breaking changes.

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[jamillambert]

This PR was created as a test of the new GitHub agent and not intended to be merged.