perf: remove unnecessary allocation when writing http dates

[robjtede]

PR Type

Perf

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

Overview

Removes unnecessary allocation when formatting HTTP Dates.

Results from divan benchmark

Before:

Timer precision: 41 ns
date_formatting     fastest       │ slowest       │ median        │ mean          │ samples │ iters
╰─ date_formatting  94.87 ns      │ 107.6 ns      │ 95.29 ns      │ 95.79 ns      │ 100     │ 100000
                    alloc:        │               │               │               │         │
                      2           │ 0             │ 2             │ 1.98          │         │
                      58 B        │ 0 B           │ 58 B          │ 57.42 B       │         │
                    dealloc:      │               │               │               │         │
                      2           │ 0             │ 2             │ 1.98          │         │
                      58 B        │ 0 B           │ 58 B          │ 57.42 B       │         │

After:

Timer precision: 41 ns
date_formatting     fastest       │ slowest       │ median        │ mean          │ samples │ iters
╰─ date_formatting  77.34 ns      │ 127.9 ns      │ 80.63 ns      │ 83.82 ns      │ 100     │ 100000
                    alloc:        │               │               │               │         │
                      1           │ 1             │ 1             │ 0.99          │         │
                      29 B        │ 29 B          │ 29 B          │ 28.71 B       │         │
                    dealloc:      │               │               │               │         │
                      1           │ 1             │ 1             │ 0.99          │         │
                      29 B        │ 29 B          │ 29 B          │ 28.71 B       │         │