feat(rpc): named-procedure RPC with OUT params and TVPs

[MattJackson]

Integrates the intent of upstream PR tiberius-rs/tiberius#328 onto current `dev`, resolving #275.

What

Implements calling a stored procedure by name (previously a `todo!()` in `rpc_request.rs`), with input params, OUT params and table-valued parameters, reconciled with the existing by-id RPC path used by `execute`/`query`.

Codec

• Encode `RpcProcIdValue::Name` as a US_VARCHAR proc name; the by-id path is unchanged.
• New `RpcValue` enum (`Scalar(ColumnData)` / `Table(TypeInfoTvp)`) replacing the raw `ColumnData` value on `RpcParam`; all existing call sites updated to `RpcValue::Scalar(..)`.
• New `TypeInfoTvp` encodes TVP type info + rows per MS-TDS 2.2.5.5.5, rewriting fixed-length column types to their nullable var-len equivalents.
• Nullable scalar values now encode a proper NULL when no `TypeInfo` is supplied.

Public API

• `Command` with `new`, `bind_param`, `bind_out_param`, `bind_table`, `bind_table_with_dbtype`, `exec`.
• `CommandStream` yielding `CommandItem` (rows, metadata, return status/value, rows affected), collectible into `CommandResult` which exposes `return_code`, `try_return_value`, `rows_affected` and result sets. RETURNVALUE tokens (already decoded on `dev`) surface as OUT parameter values.
• New `tvp-macro` crate providing `#[derive(TableValueRow)]`.

Tests

• Unit tests: named-proc RPC request encoding (proc name, param name, ByRef flag, by-id vs by-name proc slot), TVP type-info encoding, and derive-macro output.
• Integration tests in `tests/command.rs` (scalar exec, OUT params, TVPs) require a live SQL Server.

Verification

• `cargo build` (default): clean
• `cargo test --lib`: 124 passed (incl. new unit tests); `cargo test -p tvp-macro`: passed
• `cargo fmt --check`: clean
• `cargo clippy --features=all -- -D warnings`: no findings in the new/changed code (pre-existing repo lints from a newer local toolchain are untouched)

Draft because the integration tests need a live SQL Server to run.

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